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0 a. [lOBERT H.PARKER

ZOOGEOGRAPHY AND ECOLOGY OF SOME MACRO-
INVERTEBRATES, PARTICULARLY MOLLUSKS, IN THE
GULF OF CALIFORNIA AND THE CONTINENTAL SLOPE

OFF MEXICO!

With Plates I-XV
By Robert H. Parker^

Woods Hole, Massachusetts

Table of Contents

Page

Abstract 2

Introduction 4

Acknowledgments 11

History of Biological Exploration in the Gulf of California 13

Methods of Collecting and Analyzing the Data 16

Description of the Region Sampled 26

Geology and Topography 26

Sediments of the Gulf of California 29

Bottom Dissolved Oxygen Concentrations 32

Bottom Water Temperature Characteristics 37

Salinity Distribution in the Gulf of California 42

General Circulation within the Gulf of California 43

Descriptions of the Macro-invertebrate Assemblages and their environments. ... 47

I. The Intertidal and Shallow Rocky Shore Assemblage 47

n. Assemblage of Intertidal Sand Beaches and Sand Flats to 10 Meters. . . 48

III. Low-Salinity Lagoon and Mangrove Flats Assemblage 52

IV. Nearshore, Sand and Sand-Mud, 1 1-26 Meter Assemblage 53

V. Intermediate Shelf Assemblage, 27 to 65 Meters 60

VI. Outer Shelf Assemblage, 66 to 126 Meters, Clay Bottom, Southern Gulf
of California 76

1) Support for this study has been received from the National Science Foundation Grants
G-5419, G-13163 and G-20060, and funds from the Of^|jj^Naval Research, Nonr- 2216(01).

2) Scripps Institution of Oceanography, Univen^i^^r7iarTi'|(teia, San Diego, also Universite-
tets Zoologiske Museum, Copenhagen, DenmaA. Presejj^addiUs: Systematics-Ecoiogy Pro-
gram, Marine Biological Laboratory, Woods^ole, Aj^Jj^usett^

1 Vidensk. Medd. fra Dansk naturh. Foren. fid. 126.i

1939

VII. Outer Shelf Assemblage, 66 to 126 Meters, Sand Bottom, Northern Gulf

of California 76

VIII. Northern Gulf Basins and Troughs Assemblage, 230 to 1500 Meters 78

IX. Upper Slope Assemblage, Central and Southern Gulf, 121 to 730 Meters 81

X. Middle Continental Slope Assemblage, 731-1,799 Meters 84

XI. Abyssal Southern Borderland Basins and Outer Continental Slope

Assemblage, 1,800 to 4,122 Meters 85

XII. California Borderland Basins Assemblage, 1,641 to 2,358 Meters 88

Discussion 90

I. The Intertidal Rocky Shores 93

II. Intertidal Sand Beaches and Sand Flats 96

III. Low-Salinity Lagoons and Sand Flats 100

IV. Nearshore Shelf from 1 1 to 26 Meters 102

V. Intermediate Shelf from 27 to 65 Meters 115

VI. Outer Shelf, 66 to 120 Meters, Southern Gulf 120

VII. Outer Shelf, 66 to 120 Meters, Northern Gulf 122

VIII. Northern Gulf Basins and Troughs, 230 to 1,500 Meters 123

IX. Upper Slope, Central and Southern Gulf, 121 to 730 Meters 125

X. Middle Continental Slope, 731 to 1,799 Meters 127

XI. Abyssal Southern Borderland Basins and Lower Continental Slope, 1,800

to 4,122 Meters 129

XII. California Borderland Basins, 1,641 to 2,358 Meters 131

Summary and Conclusions 132

Literature Cited 135

Appendix List of Stations 143

Table I. List of Species, Depth Ranges, Station Occurrences and Environ-
ments Where Each Species Occur 149

Table II. Supplemental List of Invertebrate Species from Various Environ-
ments 1 66

Table III. Sample Devices 176

Abstract

A reconnaissance study of the zoogeography and ecology of ben-
thic invertebrates in the Gulf of California and on the continental slope
off west Mexico was carried out during the years 1958-1963. A series of
characteristic assemblages were devised for various environments found
in the Gulf of California, derived from both 272 biological samples and the
distribution of approximately 1,150 identified species of invertebrates.
Using a contingency matrix of common occurrences of 280 common species
of invertebrates, compiled by a digital computor as a basis for preliminary
analysis it was possible to designate 12 separate assemblages of inverte-
brates. These assemblages reflected distinct environmental regions of
uniform depth, sediment, water temperatures and oxygen concentrations.

These environments and their assemblages are as follows: I. Intertidal
and shallow rocky shores; II. Intertidal beaches and sand flats to 10 meters;
III. Low salinity lagoons and mangrove mudflats; IV. Nearshore shelf,
sand bottom, 11-26 meters; V. Intermediate shelf, clayey-sand to sandy-
clay bottom, 27-65 meters; VI. Outer shelf, clay bottom, southern Gulf,
66-120 meters; VII. Outer shelf, sand bottom, northern Gulf, 66-120
meters; VIII. Northern Gulf basins and troughs, 230-1,500 meters;
IX. Upper slope, central and southern Gulf, 121-730 meters; X. Middle
slope, 731-1,799 meters; XI. Abyssal Southern Borderland basins and
lower slope, 1,800-4,122 meters; and XII. California Borderland basins,
1,641-2,358 meters (limit of sampling).

The outstanding feature of the shallow water assemblages in the Gulf
of California is the great diversity of species in any one environment. A
survey of benthic communities throught the world, revealed no parallel
to this great diversity, whether in tropical or boreal regions. As many as
120 species of living mollusks were taken at numerous stations in the Gulf
in less than 60 meters. A check of unsorted dredge samples from off
Panama, revealed the same diversity there, indicating that great diversity
must be a characteristic of the Panamic province as a whole. No more
than a few individuals of any one species were taken by a grab or dredge
at any one station. Diversities were verified by cumulative curves based
on quantitative samples, compared with those made for European waters.

A preliminary survey was made concerning the relationship of general
feeding types of invertebrates to the various environments. This survey
indicated that suspension feeders outnumber other feeding types on the
shallow sandy and intertidal rocky bottoms, while detritus feeders and
scavengers outnumber other types on clayey bottoms and at greater
depths. Although this is in accordance with other communities studied
elsewhere, the Gulf of California assemblages differed in the presence of a
tremendous number of predators, which remained rather constant from
shore to abyss. The relationship between feeding types and sediment type
did not hold true in the deeper portions of the shelf, where upwelling and
associated high surface productivity are a common phenomenon. Regard-
less of sediment type in these regions, suspension feeders still predominated.
Preliminary examinations of soft parts of some of these suspension feeders
indicate that they may capture the abundant organic detritus as it rains
down from the surface. There were also indications that there is a close
relationship between environment and larval development of mollusks.
Differing larval development of mollusks also offers an explanation for
some of the disjunct distributions of many forms along the coast of Middle

America, and possibly contributes to the great diversity of species in
some groups.

Tiie distribution of shell remains in the sediments of the Gulf of Cali-
fornia gave indications as to the past history of the Gulf. Presence of
shallow-water species of shells in certain preferred depths indicated that
formerly, the sea level stood much lower than at the present time. Dates
for some of these shallow-water assemblages at the edge of the shelf, in
about 110 to 115 meters, revealed that the ages ranged from 17,000 to
19,000 years B.P. Shells of typical California province (colder) shelf
species were found in great abundance in the deeper sediments of the
northern Gulf basins and troughs. Some of these were also found in deep
waters at Cape San Lucas. This implies that during the colder Pleistocene
and lowered sea level, many species of mollusks were able to migrate
almost 700 miles to the south and up into the Gulf of California. A few
of these species were taken alive, but only in the deep areas of the northern
Gulf. Here the hydrographic conditions are similar to those now found
off California in shallower depths, since intense tidal mixing brings about
virtual isothermal and isohaline conditions from surface to bottom, with
stable temperatures of between 12° and 15°C.

Qualitative comparisons were made between macro-invertebrate assem-
blages as found in the Gulf of California and Gulf of Mexico, as well as
some counterparts in other parts of the world. The characteristic species
of the Gulf of California environments appear to have exact counterparts,
usually at the subgeneric level, in similar environments throughout the
tropics and sub-tropics of the world.

Introduction

The search for new means of recognizing ancient environments of
deposition has utilized many methods and scientific disciplines. It has
usually been assumed that the most successful way of attacking this
problem is to thoroughly understand and recognize the various modern
environments and the factors which characterize them. With this concept
in mind, a long-term study of modern sediments was instigated by the
American Petroleum Institute, under Scripps Institution of Oceanography
in 1951. The results of this study are well-known to many, being a study
of nearsbore depositional environments in the Gulf of Mexico. The author
spent some eight years in the study of the distribution of the larger or
macro-invertebrates, living in or on the bottom, using them as primary
indicators of Recent environments. These results have been published over

Fig. 1 . Place-name map of Gulf of California region.

Fig. 2a. Station locations of biological samples, Gulf of California and west coast of Baja

California.

Fig 2 b Distribution of types of sampling devices within the area of concentrated study. It
can be seen from this figure that most of the stations in the sand flat and nearshore region m
the southern Gulf and western side are grab samples. The majority of samples m the Tib^ron
region are shell dredge samples, the southern Gulf are trawl samples, the northern Gulf basm
are core samples, and most of the slope samples were taken by trawls.

8

a period of years (Parker, 1955, 1956, 1959, 1960, and Parker and
CuRRAY, 1956), and were summarized in a volume by Shepard, etal.
(1960).

The Gulf of Mexico provided one particular setting for depositional
environments, but because of its climate, geography and geologic setting,
did not include many of the modern counterparts of the ancient environ-
ments. For this, and other reasons, investigations were transferred to the
Gulf of California (fig. 1) in 1958, which in its climate, geology and geo-
graphy is a completely different type of region. Whereas the macro-
invertebrate investigations were concentrated in the lagoons, bays and
continental shelf of the Gulf of Mexico, the investigations of the Gulf
of California took place mostly in depths of 10 to 35 fathoms (18 to 64
meters) on the continental shelf, and to depths of over 2,000 fathoms
(4,000 m.) on the slope. Virtually no sampling was carried out in the
lagoons, bays and river mouths. The investigation of the Gulf of California
was also limited as to the number of stations occupied. Although nearly
2,000 biological samples were taken during the eight years of collecting
in the Gulf of Mexico, only 200 stations were occupied in the Gulf of Cali-
fornia. The present study cannot be considered more than a reconnais-
sance which gave an indication of the gross assemblages of deposition.
It will, however, give some idea of where detailed studies could be carried
out and provide a basis for a more comprehensive program.

The term assemblage is used throughout this study, since both the
living organisms and the shells and tests of previously living animals
found in the same samples were also included in the analyses. Biological
communities are generally considered an interdependent assemblage of
living animals (and plants) which are geographically bound by the various
ecological factors within a biotope. Most animal communities are regarded
as more discrete aggregations of abundant organisms, which are suspected
to be more or less dependent upon each other. Because of the diversity of
life found in most of the Gulf of California environments and the variety
of gear (most of it non-quantitative) used, one had the feeling that each
sample might be considered a separate community. It was, therefore, more
convenient to designate assemblages, loosely bound together by a number
of species, which although possibly not abundant or dominant in the
quantitative sense, are found frequently enough throughout the biotope
to be considered indicative of the biotope.

Not all of the stations occupied in this study were taken in the Gulf
of California proper, since portions of the program were carried out as a
study of the faunas of the continental slope. Those stations concerned

130' 35"

10' 90'

Fig. 3. Station locations of biological samples, continental slope from San Francisco, California
to Guatemala. Bathymetry from Parker (1961).

10

primarily with the environments of the Gulf of California are located on
figure 2 a, while the stations taken primarily on the continental slope from
California to Guatemala are shown on figure 3. As in the previous studies
in the Gulf of Mexico, many kinds of sampling devices were used (fig. 2b).
A series of Petersen and Van Veen grab samples were taken which could
be compared with grab samples from other regions, although the total
area covered by these samples (2.8 m^) is so small that no direct comparison
can be made between the Gulf of California region and other regions where
more intensive bottom studies have been carried out using quantitative
gear. The majority of shallow-water samples were taken with a small
shell dredge, towed for five to ten minutes, or otter trawls. All sizes of
trawls, the large beam trawl and the deep-diving dredge had inner net
liners constructed of the same size mesh, about 1 cm. in diameter. The
deeper stations were all taken with large beam and otter trawls or the
high-speed, deep-diving dredge (Isaacs and Kidd, 1953).

Although physical and chemical measurements were not taken with
every station, a large body of environmental data already existed from
this and other investigations of the Gulf of California. Nearly every
biological station had a sediment analysis made specifically for that station,
or an excellent sediment map existed for the region where the stations
were taken (see van Andel, et. al., 1964, in press). Depths, bottom-water
temperatures, bottom-oxygen values, and, in some cases, salinities were
also taken with the biological stations, or else the necessary data for the
specific areas sampled were available from other sources. The principal
physical factors considered in explaining the distribution of invertebrates
in the Gulf of California are, therefore, depth, sediment, bottom-water
temperature, salinity, turbulence or upwelling and oxygen.

There are also many biological factors which may be important in
limiting the distribution of benthic faunas. For this reason, some of the
research has been carried out at the Zoological Museum and Marine Bio-
logical Laboratory of the University of Copenhagen, Denmark, where a
great accumulation of knowledge on the life processes of benthic marine
invertebrates is to be found. The combination of associated physical factors,
relation to marine geomorphological features, and dependence upon
biological factors among the organisms themselves, should describe these
sedimentary environments (on a faunal basis) in such a way that the
interpretation of depositional environments of more ancient basins may
be made a little easier.

11

Acknowledgments

A large number of people both at the Scripps Institution of Oceano-
graphy and at the University of Copenhagen have contributed assistance
and ideas to this study. First and foremost, the staff of the American
Petroleum Institute, Project 51, especially J. R. Curray and T.J.
VAN ANDEL,made it possible to carry out the sampling program. Francis
P. Shepard also contributed ship time from his own portion of the
"Vermilion Sea Expedition" in 1959. R. W. Rowland, formerly of Scripps
Institution, contributed valuable assistance in the field and in the labora-
tory, making it possible to assemble the data together into some semblance
of order before the author left for Denmark. Jerry Cook, Gail Cook and
Linda Lightbowen, summer students under a National Science Foun-
dation program, also helped immeasureably in the compilation of data.

The Computation Facility, University of California, San Diego, and,
in particular. Earl Ferguson, Anna Devore, Robert and Eileen
Mitchell, were responsible for devising the computor programs used in
this study. Without their assistance it would have been impossible to
verify many of the assemblages on an objective basis.

Members of the Scripps Institution staff who contributed much of their
time and information were Carl L. Hubbs, who gave liberally of his
advice and support in obtaining funds, Richard Rosenblatt, who
assisted in the field and in the laboratory, Robert L. Fisher, who supplied
the bathymetric information, and Gunnar I. Roden, who provided much
unpublished hydrographic data from the Gulf of California.

The author is also deeply grateful to the Zoological Museum of the
University of Copenhagen for permission to use their facilities, collections
and personnel during the period used to crystalize the thoughts and ideas
in this paper. He is particularly indebted to Henning Lemche, Jorgen
Knudsen, and especially to Niels Bjarnov, for their criticisms and
assistance. Valuable ideas and information were also gained from the
University of Copenhagen, Marine Biology Laboratory, Helsingor, Den-
mark, particularly from Gunnar Thorson, who has critically read the
manuscript, A. Moller Christensen and W. K. Ockelmann.

A large number of specialists agreed to identify the invertebrate groups
which were unfamiliar to the author, and graciously donated their time
to those identifications. Without their assistance, it would have been
impossible to compile the immense list of organisms contained in this
study. A list of these specialists and the groups sent to them is appended.

12

Dr. Edward C. Allison, San Diego State College
Dr. Frederick M. Bayer, University of Miami, Florida
Dr. S. Stillman Berry, Redlands, California
Dr. Leo Berner, National Science Foundation,

Washington, D.C.
Dr. Carl Boyd, Dalhousie Inst, of Oceanography,

Halifax, Nova Scotia
Dr. Edward Brinton, Scripps Institution
Dr. William G. Clark, formerly Scripps Institution
Dr. Arthur H. Clarke, Jr., National Museum of Canada,

Ottawa
Dr. Elisabeth Deichmann, Museum Comparative

Zoology, Harvard
Dr. J.Wyatt Durham, Museum Paleontology, U. of Calif.

Berkeley
Dr. William K. Emerson, Amer. Mus. of Nat. History,

New York
Dr. John S. Garth, Allan Hancok Foundation, U. of

S. Calif.
Mr. Gilbert Grau, Hollywood, California
Dr. Janet Haig, Allan Hancock Foundation, U. of S. Calif.
Dr. Cadet Hand, Dept. Zoology, U. of California,

Berkeley
Dr. G. Dallas Hanna, California Academy of Sciences
Dr. Olga Hartman, Allan Hancock Foundation, U. of

S. Calif.
Dr. WiLLARD D. Hartman, Peabody Museum, Yale

University
Dr. Joel W. Hedgpeth, Pacific Marine Station, Dillon

Beach, Calif.
Dr. JORGEN Knudsen, Zoological Muzeum, Copenhagen,

Denmark
Dr. Henning Lemche, Zoological Muzeum, Copenhagen,

Denmark
Dr. Heinz Lowenstam, Calif. Inst, of Technology,

Pasadena, Calif.
Dr. Ernst Marcus, Universidad de Sao Paulo, Brasil
Dr. John A. McGowan, Scripps Institution
Dr. Allyn G. Smith, California Academy of Sciences
Dr. Rudolph Stohler, Zoology Dept. U. of California,

Berkeley
Dr. John D. Soule, Allan Hancock Foundation, U. of

S. Calif.
Dr. Mathilde Schwabl, Zool. Institute, Univ. of Vienna,

Austria
Mr. J. R. Thompson, U.S. Bur. Fish., Pascagoula,

Mississippi
Dr. Torben Wolff, Zoological Museum, Copenhagen,

Denmark

Hexacorallia
Octocorallia
Micro-mollusks

Salpa

Galatheaidae

Euphausiacea

Mysidae

Abyssal Buccinidae

Holothuroidea

Echinoidea

Scaphopoda

Brachyura
Pectinidae
Paguridae

Anthozoa
Conidae

Polychaeta

Porifera

Pycnogonida

Abyssal Pelecypoda

Opisthobranchiata

Brachiopoda

Abyssal Nudibranchiata

Cephalopoda

Amphineura

Amphineura

Bryozoa

Solenogasters

Peneaeidae

Isopoda

13

Dr, John Yaldwyn, Australian Museum, Sydney,

Australia Decapoda (shrimp)

Prof. C. M. YoNGE, University of Glasgow, Scotland Mollusca

Mr. Fred C. Ziesenhenne, Allan Hancock Found., U. of

S. Calif. Ophiuroidea and

Asteroidea
Dr. Victor Zullo, Marine Biological Laboratory,

Woods Hole, Mass. Cirripedia

Most of the illustrations in this paper were done by Niels Bjarnov,
James R. Mori arty, and SP6 Joseph Freitas (United States Military
Assistance Advisory Group in Denmark). The illustrations on faunal
plate X were drawn by artist Poul Winther of Copenhagen. The photo-
graphs on plates XI-XV were supplied by Dale Krause, University of
Rhode Island.

History of Biological Exploration in the Gulf of California

Considering the size of the region, comparatively little biological col-
lecting has been carried out in the Gulf of California. Few areas along the
coast are readily accessible to the average biologist, and until a few years
ago, no marine stations had been established along the coast. There is now
a small station. The Vermilion Sea Field Station, at Los Angeles Bay,
Baja California, established by the San Diego Natural History Society,
Considerable biological research is now being conducted there in a number
of fields (McLean, 1961). There is also a small marine station operated by
the Mexican Government at Mazatlan, Sinaloa, although little research
has been carried out there, apart from assembling a small study collection
of local marine animals.

Early collections from the Gulf of California and the Pacific coast of
Middle America consisted mostly of moUusks. In the early 1800's, col-
lections of mollusks were made by a business man, Hugh Cummings, who
sent a vast collection back to Europe. This collection was eventually
acquired by the British Museum of Natural History. Many of the moUusk
species collected and identified in this present study were originally
described from the Cumming's collection by such early taxonomists as
Broderip, the Sowerbys, Hanley, Reeve and Deshayes. An historical
account of this collections can be found in Olsson (1961). Collections were
also made by Colonel Ezekiel Jewett, and later described by Philip
Carpenter (1855-57, 1863, 1864). Other early moUusk collections were
carried out by C. B. Adams (mostly in Panama) and Frederick Reigen,
a Belgian who lived in Mazatlan. These collections were also described
by Carpenter (1864). The mollusks described by C. B. Adams have been
figured and his descriptions duplicated in Turner (1956).

14

The first major expedition for the purpose of general biological collecting
into the Gulf of California was carried out by the U.S. Fish Commission
steamer Albatross under Alexander Agassiz in 1891 and again in
1904-05. Many of the stations occupied by the Albatross were taken in
deep water, and most of the deep-water invertebrate species (especially
the moUusks) collected during this present study were originally collected
and described through the efforts of the "Albatross Expedition". A com-
plete list of stations and the early papers resulting from this expedition
can be found in Townsend (1901). A final expedition into the Gulf of
California by the Albatross was undertaken in 1911, these results being
again reported by Townsend (1916). The papers resulting from this series
of expeditions by the Albatross provide by far the greatest existing
accumulation of data on the animals living in the deeper portions of
the Gulf.

Between 1929 and 1931, Herbert N. Lowe carried out a number of
moUusk collections in the Gulf of California, which were later described
by him and also by H. A. Pilsbry. A list of these papers may be found
under the respective authors in Keen (1958). Most of the moUusks de-
scribed by Lowe are in the San Diego Museum of Natural History, and
served as a basis for comparison in the identification of the present
collection.

The 1921 expedition to the Gulf of California by the California Academy
of Sciences provided additional information on the biology of the flora and
fauna of the Gulf. These results were published by a number of investigators
including Baker (1926), Baker and Hanna (1927), Oldroyd (1918) and
Slevin (1923). The "Templeton Crocker Expedition" of the New York
Academy of Sciences in 1936, under William Beebe (1937), provided
new information on moUusks and decapods, as well as many other in-
vertebrate groups from intensive dredging and shallow-water collecting.
The moUusks were described in great detail, along with abundant eco-
logical information by Hertlein and Strong (1940-1951). Papers dealing
with the other invertebrate groups may be found in Zoologica, the publi-
cation of the New York Zoological Society, in the years from about 1940
to date. A rather large collection of intertidal invertebrates was obtained
by the "Steinbeck-Ricketts Expedition" of 1939. Some of the data re-
sulting from this trip was included in the narrative of the expedition by
Steinbeck and Ricketts (1941).

The next major expedition into the Gulf of California, and the first one
to study the oceanography and geology of the Gulf was the 1939-1940
"E. W. Scripps Cruise to the Gulf of California", under the sponsorship

15

of the Geological Society of America and Scripps Institution of Oceano-
graphy. The results of this cruise, including the paleontology and some
biology, are summarized in Anderson, etal.{\950). A later list of the
mollusks collected by this expedition can be found in Emerson and
Puffer (1957), and a further reworking of some of the geological data can
be found in Byrne and Emery (1960). Several expeditions were also made
into the Gulf of California by the Allan Hancock Foundation with the
VeleroIII and IV (Eraser, 1943). The biological data from these
cruises has been published at various times by Garth, Haig, Ziesen-
HENNE, Grau, Soule and others in the Allan Hancock Pacific Expeditions
Reports, Volumes 1 to 23. Information on stations collected by the Allan
Hancock Foundation subsequent to 1942 can be obtained from the
Foundation.

Finally, the last major collecting cruise into the Gulf of California prior
to the present "Vermilion Sea Expedition" was the "Puritan-American
Museum of Natural History Expedition" in 1957. A general
account of the expedition can be found in Emerson (1958), who has also
written several short papers on the Pleistocene mollusks of the region,
resulting from the efforts of this expedition. Squires (1959) gives an ex-
cellent account of the corals collected on the Puritan cruise and Soule
(1961) has discussed the bryozoans.

Small collections of mollusks have been made from time to time by
moUusk collectors at Puerto Peiiasco, San Felipe, Guaymas, La Paz and
Mazatlan, Mexico, although references are too numerous to be given here.
Dr. S. Stillman Berry has described many new species of mollusks from
the Gulf and has discussed their biology in his Leaflets in Malacology
(privately printed and available from Berry). Notes on Gulf of California
mollusks can also be found in the Annual Reports of the American Malaco-
logical Union, Pacific Division. The collections of Mrs. Faye Howard of
Pacific Palisades, California have provided the basis for lists by a number
of people, including McLean (1961), and her notes on the reproduction
of marine gastropods from the Gulf of California were made available to
the author through Professor Gunnar Thorson. One other expedition to
the Gulf of California in recent years should also be mentioned, "The
Ariel Expedition", undertaken by members of the Conchological Club of
Southern California. Using a shrimp boat, a number of excellent collections
were taken on the middle and outer shelf portions of the Gulf. An account
of some of the mollusks taken can be found in Shasky (1961).

Although scattered, there seems to be considerable literature available
on the biology of the Gulf of California. Not mentioned above are also a

16

few papers on the biology of commercial shrimp written under the Mexican
fisheries investigations, and a large number of papers on fisheries biology
and primary production by biologists working under the California
Cooperative Oceanic Fisheries Investigations and the Bureau of Commercial
Fisheries of the U.S. Fish and Wildlife Service. None of the above studies
has attempted an overall ecological analysis of the Gulf of California,
although many do discuss the zoogeographic divisions of the Gulf as
related to various floral and faunal groups. Two issues of Systematic
Zoology, published in 1960 (Garth, etal., 1960) were devoted to a sym-
posium on the zoogeography of the Gulf of California.

Methods of Collecting and Analyzing the Data

Collections of biological material for this study were made during the
period from November, 1958 through November, 1961 by a number of
expeditions. These expeditions were: "Tuna Oceanographic Cruise
11", November, 1958; "Vermilion Sea Expedition I", April-May,
1959; "Vermilion Sea Expedition 11", May-June, 1959; "Ver-
milion Sea Expedition-Shepard", April, 1959; "Southern Bor-
derland Cruise III", February, 1960; "Curray-Orca Cruise",
March-April, 1960; "Holt Expedition", December, 1960; "Baja
Slope Expedition", May, 1961; and "Curray-Gulf of California,
Winter Cruise", November, 1961, all made under the sponsorship of
Scripps Institution of Oceanography. Cruises "AEC-l", March, 1960,
"AEC-2", March-April, 1960, and "AEC-3", November, 1960, were
carried out by the Advanced Systems Development Division of Pneumo-
dynamics Corporation, El Segundo, California.

Since none of these cruises was undertaken for the specific purpose of
benthic biological sampling, with the exception of the "Baja Slope" and
"Holt" expeditions (both in the Pacific on the west side of Baja Cali-
fornia), sampling was somewhat haphazard, depending entirely upon when
time was available for sampling the benthos. Most of these cruises were
primarily geological or geophysical in nature. No systematic program for
the collecting of quantitative grab or bio-mass samples could be carried
out, although a number of orange peel and small Van Veen samples were
taken on "Vermilion Sea Expedition I", and a few Petersen Grab
samples were taken by the author during "Vermilion Sea Expedition-
Shepard". All other samples were taken either with various dredges and
trawls or by diving and hand-collecting. Some conception of the principle
mode of sampling for each environment sampled can be gained from

17

figure 2b, and Table III. All grab samples were washed through a series
of sieves, the smallest diameter of the screens being 1 mm, while a uniform
inner mesh size was used in all trawls, regardless of trawl dimensions. The
type of gear used at each station taken is given under the station data in
the appendix. All material living and dead was retained, and after thorough
sorting, all animals groups which could not be identified at Scripps Insti-
tution were sent out to various specialists mentioned in the acknowledg-
ments. The author sorted all samples into the various systematic groups
before sending to specialists, and personally identified 95 "^/q of the mollusks.
Some small groups of mullusca were sent to specialists for verification.

It was obvious after a short time, that the volume of data collected
during this program was too large to handle in a conventional manner.
First of all, over 1,150 species of invertebrates were identified, and at least
another third are yet to receive names. Altogether over 270 stations were
taken, although only 200 were taken in the Gulf of California. Each station
was characterized by date, time collected, depth, latitude, longitude,
bottom temperature, bottom oxygen, sediment type, collecting device
and the organisms found there. When attempting to put this information
together, it could be seen that there were too many variables to integrate
by inspection alone. At about the time when it became necessary to process
this information, an electronic digital computor (a Control Data Systems
1604) was installed at the School of Science and Engineering, University of
California, San Diego. Since the data from the geological studies of the
Gulf of California were already being entered on to IBM cards and programs
written to process their data, it was suggested that the biological data
could also be processed in a similar manner.

It was first necessary to construct a system for putting the information
on to IBM cards, so that the maximum use of the data could be made with
a minimum number of cards. Three sets of cards were found to be sufficient
for recording all of the data. The first set of cards was for the storing of
station data (an example of the print-out is shown in figure 4a). Originally,
many of the stations had different sets of numbers, corresponding to the
various expeditions. Later in this study, all early stations were numbered
consecutively, and additional stations added in the same numbering
system. Each station card contains station number, date of collection,
time of collection, depths, latitudes and longitudes to tenths of minutes,
bottom water temperatures to tenths of degrees Centigrade, oxygen values
to tenths of a ml/L., sediment types (using code numbers devised by the
geologists), collecting devices, also coded, total number of species taken
at the station, and total numbers of living and dead individuals per station.

2 V'idensk. Medd. fra Dansk naturh. Foren. Bd. 126.

18

y =r-;:y^-^->r.-.i-ss- "^i p g '-Hrsj tt^-^yyr:

< »s. ^g (V' f- If e

* *^ f^fTi; 1^ f.. y. y. '^ '

DT5 c C3 OTST!

; o-c i^'c »» i

5S§888*g-88«*S&fe8-?&&§-*^-§8-g»*6-8^88SSS«-&§-§f

— ' So 7;S S S S S ^r g 5 g 6 p'g-r-5rg-g 3€ cH^ S-r o-S C---Ji C* " ? -fS^? c"?'^-£"SP*"S"^>JP^''""?S'c « -J^JI

^ft.ft^ftt,ft.ft.f>^^^fli^v;f^.^.f■^.^.^^^r.r^f^^<>ftM■^^A.^.^^.^^fr, ^w- r^ r> f^. fv f^f^ r. p. iN^ (V ^ ^.»^i.^,g^ft, At N '^ ^ ^JJ J^."** *V,^ rv**^

ff-e-#-' e 'c e'

Fig. 4a. Samples print-out of IBM station-data cards. This photograph of the first set of cards

does not agree with the data as shown in the Appendix, as the depths have recently been

changed from fathoms into meters.

A second card is used as a storage card for the data on the individual
species. This card contains a species code number, which gives the class,
genus and species, with enough digits for the largest possible number of
classes, genera and species to be added. These cards are numbered con-
secutively, but correspond to an alphabetical listing by genus and species.

19

1
1

u

It -

„

"T-

i t

J

n

n-"-"

•^ ^ ■a

gllE

V 9 <:

^^Z

w *

Sil-.^

Fig. 4b. Sample print-out of IBM species-data cards.

The cards were later re-sorted systematically for printing. The total
number of station occurrences of each species is listed next and, finally,
all station numbers at which each species occurred, plus the number of
living and dead individuals for each species at each station (fig. 4b). The
third card was devised to be paired with the species data card and contains
the identical species number, a letter designating the class or phyla, and
the complete scientific name to subgenus and species (fig. 4c). This last

20

^ o go J

JTifv W -« S^ o ~ "* »~

« — >- «>'X«IJD'"ae
iiarxvoQixxix •

?g:

: ifc » V ^ r jE tt

- -: t- c -

Fig. 4c. Sample print-out of IBM species-name cards. This is an old listing with occasional
errors, and arranged alphabetically. The cards are now arranged systematically.

card permitted the printing of the correct scientific name of all species
dealt with in any program analyzing this data. All of these data were
entered on IBM cards in approximately two months with the help of
students. One set of cards, which can be quickly duplicated at virtually no
cost, is kept at Scripps Institution and may be obtained on request. A
second set of cards was taken to Denmark, where it could be used for
additional analysis in Copenhagen.

21

Two programs for handling these data were then written by programmers
in the Computation Facility of the University of California, San Diego,
using Fortran as the machine language. The first program was written
as a test of whether this system of data storage could be used satisfactorily
for grouping together species into natural classifications as related to the
distribution of physical factors. Earl Ferguson of the Computation
Facility wrote most of the program, with some assistance from Anna
Devore. The computor was programmed to list all species found at various
depths, temperatures, oxygen limits, sediment types and geographic
localities. Unfortunately, the limits of these variables were chosen arbi-
trarily, based on previous inspection of the data. The computor first listed
all stations falling within the various ranges of each variable, using station
cards only. The next step entailed a search through all of the species-data
cards, in which the machine stored the numbers of all species occurring
at all stations previously listed for each category. Finally, all species
numbers were matched with the species-name cards, and complete print-
outs were made of all the species names occurring under each increment of
depth, temperature, oxygen, sediment type and geographical region
(example on fig. 5a). The entire operation, taking 28 minutes, would have
taken several months by hand. The next step in determining the influence
of various physical factors on the distribution of invertebrates would be
to have the machine choose the limits of the variables by a multi-correla-
tion analysis. This has not been done as yet, since a somewhat simpler
method was devised for a preliminary analysis of the assemblages.

The second program was modified from one originally written for
Edward Facer of Department of Oceanography at Scripps Institution,
and was written by Robert and Eileen Mitchell. Facer's program
was devised for data catalogued in a somewhat different form, and so had
to be rewritten to utilize the present data. Facer (1957, 1963) demonstrated
that through a contingency matrix of joint occurrences of common species,
using the geometric mean of the proportion of co-occurrences, that cer-
tain natural groupings of animals would result from a sampling of a
region, which would correspond to environmental boundaries. Using only
the presence or absence of species at every sample location, minus a
term that corrects for sample size, the computor was asked to produce
statistically valid groupings from 350 species taken more than five times
in this sampling program. The other 800 species taken in this study were
considered too infrequently taken to be considered in this analysis. The
computor program, which did not take into account type of sampling de-
vice, first compared the distribution within the 270 stations of every spe-
cies with every other species. Pairs of species, with pre-established lower

22

;3S:

Fig. 5a. Print-out of one of the results of the computer program which listed all species taken

as they occurred in various increments of depth, temperature, oxygen, etc. This example gives

all species taken in between 500 and 1,000 fathoms.

limits of common occurrences, were produced by finding out at which sta-
tions every species occurred with any other species. For instance, species
"A" may have been talcen at 30 stations, while species "B" may also have
been taken at 15 of the same stations, although occurred at a total of 40
stations. At these same 15 stations, several other species may also have

23

Fig. 5 b. Print-out of the first page of the results of the matrix program. Numbers in headings
of columns are index numbers corresponding to species code numbers of 139 abundant species.

been taken with the first two, but were taken jointly with other species and
combinations more frequently at other stations. Eventually, with nearly
20 million operations, every species and combination of species was com-
pared with every other species and combination at every station (See fig.
5b). Altogether, 53 species were found to be affiliated with a minimum
of six others in the first matrix of species with more than 8 station oc-

24

currences per species. Another 22 species formed combinations of not less
than three species with those species having between five and seven
occurrences. Since almost every index species listed for one group may also
be part of several other groups, in actuality, only 10 or 12 valid distinct
groupings of species resulted. Most of these groups occurred on the conti-
nental shelf in from 11 to 126 meters.

The next step in producing stations and faunas which characterize
particular environments, was to perform a separate analysis by personal
inspection of the index groups with the largest number of associated
species. This was done by listing all species in each group, and then listing
all station occurrences at which each species was taken, living only,
although the computor program was based on both living and dead
occurrences. It was then possible to determine only those living species
which were important components of the station groups. Those stations
which proved to have a large number of commonly associated living species
were then examined as to location and common physical factors. For-
tunately for this study, most of the resultant station groupings were very
distinct, both as to geographical location and the same range of physical
factors. Therefore, instead of attempting to determine what species oc-
curred in any one set of physical factors, the matrix actually provided
sets of stations with common physical attributes, bound together by index
or important living species. Finally, all living species taken at these
characteristic stations were listed, and those with the most station oc-
currences within the group of stations were listed for various environments
as given in Table II. In some cases, particularly environments I, II, IV
and V, lists of index species as given directly by the computor program
are given in the text, in order to show that there were certain species
occurrences which tied these stations together. More often than not,
however, these lists did not represent either the most characteristic species
nor the common living ones, and the somewhat more subjective analysis
which produced the lists in Table II, are more reliable indicators of
environment. The computor method itself appears to be an excellent tool
for defining environmental and faunal boundaries as pointed out by
Fager (1963). Unfortunately, the sampling as produced by this project
was inadequate to do justice to the problem. As can be seen in Table III
(the lists of sampling devices for each environment), a strong bias will be
produced as to the kinds of animals which will predominate in each
environment. Certain areas were sampled primarily by shell dredges,
others by large trawls, and one by grab samplers (fig. 2b). Although most
of the environments were sampled by a variety of instruments, there were

25

not enough stations taken by each type in each environment to permit
strictly vahd comparisons between either environments within the Gulf
of California region or other environments in other parts of the world.
The results as given here, do give one an idea of some of the animals living in
the various parts of the region, which from a strictly zoogeographical view-
point is valuable, since few studies have been made in one region from
shore to over 4,000 meters. The text of this program and sample results
can be obtained from the author or Scripps Institution of Oceanography.

The stations and consequent species groupings for the various environ-
ments in the Gulf of California, correspond very closely to environments
which were thought to exist from the subjective appraisal of these data.
These computor groupings were devised by almost a purely mathamatical
process, which will give nearly the same result regardless of operator. Once
the program had been written, new data could be added quickly and the
matrix repeated in a few minutes of machine time. It would have taken
many months to carry out this analysis by hand or by personal inspection,
which would also provide almost unlimited opportunity for error. The
program would have been infinitely more useful, if the stations had been
more numerous and of equal size, since the results could have been further
substantiated by abundance of individuals, as well as by mere presence
or absence.

Of importance to the paleontologist is the fact that a similar paleo-
ecological program could be carried out in older sediments from nearby
localities if the fossil sampling is detailed enough. For instance, in areas
such as the Pliocene or Miocene of Panama, Costa Rica, Columbia and
Ecuador, where many of the same species or ancestors of the same Gulf
species occur in large numbers and in varying environments, a similar
matrix of common occurrences could be constructed, giving certain units
of each formation uniform characteristics based on a common set of
species. These sets of species could then be compared to those assemblages
given here, with the hope of identifying similar environments of deposition.
It is also possible to submit data from the previously mentioned Gulf of
Mexico studies to a similar analysis, in order to substantiate the more or
less subjective analyses performed before. A wealth of paleontological
information exists from borings and outcrops of Miocene to Pleistocene age
along the Gulf of Mexico coast, which could be compared by computor
techniques to those results obtained from the sampling of the Recent.

Besides the computor analysis of these data, several other methods were
used to establish the various assemblages in the Gulf of California. About
350 areal distribution maps of common species were drafted and com-

26

pared with the distribution of the various ecological factors. A graph of
the depth ranges, both living and dead (Table I - Appendix) for all
1,150 species identified so far was devised in order to obtain an indication
as to where the majority of species were concentrated. The complete
scientific names of all species taken in this study can also be found in
Table 1. For this reason, describer and date of description has been omitted
from species names in the main body of the text. The geographic and depth
ranges of most of the important species found in this study were also
checked against the known ranges in the literature (Keen, 1958; Olsson,
1961 ; and various papers resulting from the Albatross expeditions). The
preliminary discussion of the purely biological factors which may in-
fluence the composition of the various assemblages resulted from examin-
ation of some of the original material, a survey of existing literature on
closely related species of invertebrates from tropical regions, and from
discussions with the staff of the Copenhagen University Zoological Museum
and Marine Biological Laboratory in Denmark.

Description of the Region Sampled

The majority of the biological samples collected under this Scripps
Institution survey were taken in the Gulf of California proper, or a region
which is tectonically related to the Gulf of California. This consists of the
Gulf of California itself, bounded by the peninsula of Baja California on
the west, the Colorado River delta on the north and the mainland coast
of Mexico to approximately Mazatlan, Sinaloa (fig. 1). It should also
include the Tres Marias Islands, the large irregular basins to the north and
south of these islands, and coast of Mexico to Bandaras Bay, since this
region is tectonically part of the whole complex.

Geology and Topography.

A description of the bordering geology and geomorphology of the Gulf of
California region received considerable treatment by Anderson (1950)
and by Byrne and Emery (1960). It is sufficient to say that, in contrast
to the region studied previously by the author in the Gulf of Mexico, very
few broad alluvial plains with abundant rainfall and river discharge are
present along the coast of the Gulf of California. Much of the Gulf is
surrounded by high mountains, with precipitous peaks descending almost
to the shoreline. Rocky shores are particularly abundant along the Baja
California coast, whereas broad, sandy beaches and mudflats are restricted
to the Colorado Delta area, the Costa de Hermosillo and Costa de Nayarit

27

(CuRRAY, in VAN Andel, d a/., in press). There are many small pocket
beaches on both sides of the Gulf, which do provide a niche for sandy-
beach fauna, but sandy beaches are not as extensive as they are along the
coast of the Gulf of Mexico.

Estuarine coastal lagoons are rare in the Gulf of California proper,
which receives virtually no rainfall, but very large lagoons are to be found
south of Mazatlan, where the climate becomes humid. Information con-
cerning these lagoons was obtained from Fred B Phleger and Joseph
R. CuRRAY (oral communication), and from the literature, particularly
Keen (1958). There are a number of semi-enclosed bays on the west side
of the Gulf, where normal Gulf conditions occur, and a few strictly tidal
to hypersaline lagoons on the east side from Guaymas to the north. There
are also some very large lagoons near the vicinity of Los Mochis (fig. 1).
Little is known concerning their fauna. The configuration of the shoreline
of the Gulf of California is so variable that a tremendous number of
ecological niches are present for marine and intertidal invertebrates.

The continental shelf region was sampled in considerable detail, although
in only two main regions, namely, off the Costa de Hermosillo and Costa
de Nayarit. Here the shelves are relatively broad and gently sloping,
providing niches for many assemblages which parallel those found on the
broad shelves of the Gulf of Mexico. On the other hand, the rocky and
sandy continental shelf on the west side of the Gulf of California from
Angel de la Guarda Island to Cabo San Lucas (fig. 6) is very narrow, and
in some places virtually non-existent. The west side of the Gulf is therefore
inhabited primarily by epifaunal species of invertebrates, since little
soft level-bottom area is available for infaunal species. Alternatively, the
upper Gulf, north of Tiburon and Angel de la Guarda Islands, is very
similar to the Gulf of Mexico shelf. One fairly deep, broad basin (Tiburon
Basin) exists between the islands, but in general there is a broad, gentle
shelf descending from the Colorado delta to depths of about 200 meters

(fig. 6).

In contrast to the strictly northern portion of the Gulf, the southern
and central portions are characterized by deep channels and basins, with
steep rocky sides descending to over 2,000 meters. The bottom of the basins
themselves are flat, but the total area suitable for level-bottom communi-
ties is rather small compared to the total area of the Gulf. The bathymetry
of the Gulf of California was first drawn up in detail by Shepard (1950),
based principally upon soundings obtained on the "E. W. Scripps
Cruise" in 1940. Byrne and Emery (1960) gave a simplified version of
this chart, but added no new information. A new chart of the bathymetry

28

Fig. 6. Bathymetry in fathoms of the Gulf of California. Contours from Fisher, Rusnak and
Shepard (van Andel, et a/., 1964. in press).

29

of the Gulf of California has been compiled by Robert L. Fisher, Gene
A. RusNAK and Francis P. Shepard (van Andel, etai, in press), based
on new soundings obtained on the various "Vermilion Sea" expeditions.
A simplified version of Fisher's chart is shown in fig. 6. The bathymetry
of the continental slope and abyssal regions from California to Panama is
shown on figure 3.

Sediments of the Gulf of California.

A general description of the sediments of the Gulf of California, based
on 310 samples taken by Scripps Institution on the "E. W. Scrip ps Cruise"
and by various cruises of the Allan Hancock Foundation, is given in Byrne
and Emery (1960). A more detailed map of the sediments has been com-
piled by van Andel et al. (in press). Both are in relatively close agreement
as far as the gross sedimentary characteristics of the Gulf are concerned,
although many more sample analyses are involved in van Andel's version
and the one prepared by him for this paper (fig. 7). Curray in van Andel
et al. (in press) has drawn up detailed charts of the sediments for the two
areas most important to the biological studies (Costa de Hermosillo and
Costa de Nayarit). These charts are based on grain-size analyses and other
sedimentary properties (fig. 8 reproduces one of these). Using these charts,
it is possible to trace the close correlation between certain macrofaunal
communities or assemblages and sediment type.

According to Byrne and Emery (1960, pp. 996), the sediments of the
subtidal portions of the Gulf can be described in the following manner. The
extreme northern end in the vicinity of the old Colorado River mouth is
characterized primarily by silty sand (based on a nomenclature devised
by Shepard, 1954). Proceeding south to a point midway between the two
large islands in the Gulf, the sediments change to silty clay, the typical
sediments for shrimp fishing grounds both in the Gulf of Mexico and Gulf
of California. The area which marks the transition between the northern
and southern Gulf in the vicinity of the Tiburon Basin is predominately
sand. More detailed sampling as a result of the Vermilion Sea ex-
peditions (in part, fig. 8) in the area shows a great range of sediment
types, ranging from rock and gravel to silty clay, although there is a
preponderance of sandy sediments. The rest of the central and southern
portion of the Gulf below 200 meters is characterized by both Byrne and
Emery and van Andel as silty clay. There are a few patches of clayey
silt on some of the topographic highs, and portions of the Guaymas Basin
are covered with diatomaceous sediments.

Detailed sediment maps of the shelf portions of the Gulf south of
Tiburon Island and Angel de la Guarda Island are almost impossible to

30

Fig. 7. Sediments of the Gulf of California, based only on size analysis of samples taken on

Vermillion Sea Expeditions 1 and II. Sediments classified according to Shepard (1954).

(After VAN Andel, in press).

31

28*i0 112'

DEPIH CONTOURS

Fig. 8. Sediment distribution for the Costa de Hermasillo region, south of Tiburon Island.

Depth and sediment countours based on a chart drawn up by Joseph R. Curray, Scripps

Institution. Shelly zone added by this author.

construct from the available data, except for the two broad portions stu-
died by Curray in van Andel, et. al. (1964, in press). On the west side,the
bottom is primarily rock, gravel and sand. There is no source of fine
sediment, and with the steep sides of the shoreline and violent weathering,
one can expect to find only coarse to very coarse sediments. As mentioned
before, the northern portion of the Gulf continental shelf is characterized

32

by finer sediments, deposited by previous fluvial cycles of the Colorado
River. Where there are steep sides and rocky headlands on the east or
mainland side of the Gulf, the sediments are again coarse and sandy. If the
shelf broadens, the sandy sediments soon disappear, being replaced by
clayey silts and silty clays on the outer edges of the shelf (fig. 7). However,
two areas where this is not the case are those studied by Curray off
Hermosillo and San Bias (figs. 7 and 8). Both of these broad shelves are
at least partially a result of the growth of large river deltas during Holocene
lowered sea level, plus subsequent inundation, re-working and high rates
of deposition during the last rise of sea level during the past 19,000 years
(Curray, 1962). The conditions which produced these submerged deltas
have therefore complicated the sediment distribution so that both areas
are characterized by small patches of varying sediments irregularly
distributed. This patchiness of coarse and fine sediments has also produced
considerable patchiness in the distribution of the invertebrates. The
faunal communities are not located strictly parallel to each other in
descending depth as in the Gulf of Mexico, but often run in confused
patterns, mostly related to sediment size.

Bottom Dissolved Oxygen Concentrations.

Fortunately for this study, there existed a considerable body of in-
formation on the hydrography and physical oceanography of the Gulf of
California. Beginning with the "E.W.Scripps Cruise", a number of cruises
have been undertaken to the head of the Gulf solely for the purpose of
measuring various hydrographic factors. Most of these cruises were carried
out by Scripps Institution in collaboration with the South Pacific Fisheries
Investigations of the U.S. Fish and Wildlife Service and the California
Cooperative Oceanic Fisheries Investigations. The results of the first
seven cruises were discussed in detail by Roden (1958) and Roden and
Groves (1959). Since that time, several more cruises have been carried out
under the same program, in addition to which hydrographic data was col-
lected by the "Vermilion Sea Expeditions" and various "Tuna Oceanography
Cruises" sponsored by the Saltonstall Fund studies at Scripps. Although a
number of cross-sections were given in the published studies of oxygen
distribution in the Gulf, there was no discussion of the areal distribution of
bottom oxygen. The present author compiled the raw data for all known
deep casts, averaged the bottom values for all of the stations where data
existed (fortunately, the same stations were occupied at almost every
season and on several occasions), and plotted them on a bathymetric
chart of the Gulf of California (fig. 9). No attempt was made to obtain

33

an accurate picture of oxygen variation in the very shallow waters, but it
was possible to get some idea of average oxygen concentration at all depths
from over 3,000 meters in the entrance of the Gulf to about 40 meters along
the coast (fig. 9).

These data were first isoplethed at .5 ml/L. intervals, and then smoothed
out to give the picture of oxygen distribution as shown in fig. 9. As can
be seen in the northern Gulf, there is normally an orderly progression from
high oxygen to low oxygen from shallow to deep water, but the presence
of the "oxygen-minimum zone" from Tiburon Island to the south com-
plicates the picture considerably. Values drop suddenly at about 100 to
200 meters to below .5 ml/L., continuing with low values to depths of
about 1200 meters, where they rise to 1 ml/L. in the southern basins and
even higher at the entrance to the Gulf. One exception to this pattern can
be found in the Guaymas Basin, where there is less than .5 ml/L. at the
bottom. This basin also contains the largest concentration of diatomites.
These diatomites are finely layered, and show no signs of disturbance by
burrowing organisms. The lack of animals necessary to disturb layered
sediments can probably be attributed to the absence of enough oxygen
to sustain macro-invertebrate life. Similar adverse conditions have been
described by Emery and Hulsemann (1962) in the Santa Barbara Basin
in the continental borderland off Southern California. This basin is some-
what shallower (550 meters), but oxygen values are quite similar and even
lower than the Guaymas Basin, ranging from .5 ml/L. at sill depth of 475
meters to .1 ml/L. at the bottom. As in the Guaymas Basin, sediments are
neatly layered, showing graded deposits resulting from turbidity current
deposition, interspersed with alternating diatomite and terrigenous deposits.
Upwelling and related high plankton productivity although not on a seasonal
basis brings about a depletion of oxygen at the bottom, as in the Guaymas
Basin. Thus, during times of very low oxygen, fine layers are preserved
owing to lack of benthic organisms. During non-upwelling portions of the
cycle, there is an increase in oxygen permitting the existence of burrowing
animals which destroy some of the laminae. The primary difference be-
tween the Santa Barbara Basin and Guaymas Basin is that oxygen
depletion seems to be more or less permanent in the Guaymas Basin, since
no disturbance laminae occurred anywhere in the Guaymas cores, and no
signs of life have been found in dredge samples.

The areas with lowest oxygen values on the upper portions of the slope
of the Gulf of California can be correlated quite closely with the areas of
intense upwelling and associated plankton or diatom blooms, as shown
in fig. 10 (taken from Roden and Groves, 1959, and Byrne and Emery,

3 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

34

y

OXYGEN MINIMUM^
ZONE

Fig. 9. Dissolved oxygen concentrations, Gulf of California, based on several hundred obser-
vations, taken at various seasons over a 20-year period.

35

Fig. 10. Areas of upwelling and accompanying phytoplankton blooms in the Gulf of California,
compiled from Byrne and Emery (1960) and Roden and Groves (1959).

36

1960). The tremendous plankton blooms (Byrne and Emery, 1960),
which have been observed since the Spanish originated the name "Ver-
milion Sea" for the red tides in the Gulf, account for the extremely high
production of all forms of surface life in the Gulf from whales down to
small invertebrates (Steinbeck and Ricketts, 1941). These same con-
ditions are also found in the Gulf of Tehuantepec, investigated by the
present author as part of this study. Because of the almost hurricane
strength winds which sweep across the Isthmus of Tehuantepec, throughout
most of the year, a semi-permanent upwelling dome occurs in the Gulf,
much of it overlying the continental slope. Dredges taken in depths of
from 200 to 1,000 meters in this region produced no typical benthic life,
but large amounts of semi-fossilized wood, completely unaltered leaves,
pine cones and fish bones were obtained. Goldberg and Parker (1960)
investigated the chemical composition of the bottom waters and the age
and composition of the phosphatized wood. It was quite evident that at
these slope depths where no life and well-preserved floral and faunal
remains were found, oxygen was almost non-existent, but phosphate was
very high. Those portions of wood buried in the sediment and still in a
fresh condition, proved to be older than 28,000 years B.P., as determined
by C-14 age-dating by Hans Suess of Scripps Institution. The antiquity of
the wood would lead one to believe that the bottom oxygen-minimum
conditions along the coast where upwelling is now present have existed
for a long time. Wood in similar state of preservation was also found in
roughly the same depths along the east side of the Gulf of California from
Mazatlan to Guaymas.

A complete reversal of the depleted oxygen situation exists in the San
Lorenzo and Ballenas Channel region between Angel de la Guarda Island
and the islands to the south and the coast of Baja California (fig. 9). The
depths of this channel range from 1,000 to over 1,500 meters (500 to
800 fathoms). Throughout most of the rest of the Gulf these depths are
characterized by very little to almost no oxygen at the bottom. However,
because of the tremendous tidal transport through this narrow strait,
turbulence is effective throughout the whole water column and oxygen
values are between 1 and 3 ml/L., which is sufficient to sustain almost any
form of marine life. This phenomenon has been discussed by Roden and
Groves (1959, pp. 17-19). It might be mentioned here that the high oxygen
concentrations in this channel support a fairly rich fauna including a
number of species of solitary corals.

The faunas at the southern, deep part of the Gulf also reflect the high
oxygen conditions, which appear to be related to the underlying deep

37

Equatorial Pacific bottom water. Trawls taken in the region marked by
the 1 and 2 ml L. isopleths in fig. 9 in the southern Gulf were exceedingly
rich, and roughly of the same composition as those taken in slope depths
elsewhere along the coast of Middle America. However, fewer numbers
and kinds of animals were taken in the central Gulf basins which have
lower oxygen values.

The oxygen concentrations on the continental shelf portions of the
Gulf of California are not quite so important in influencing the faunal
assemblages, as they are at least over 1 to 2 ml/L. As shown in fig. 10,
there are areas along the shelf where upwelling does occur, and oxygen
may occasionally be depleted fairly close to shore. This is especially true
north of Mazatlan, where the oxygen-minimum zone on the bottom comes
quite close to shore despite the width of the shelf. This condition seems to
influence the faunal assemblages which change considerably north of
Mazatlan in depths of from about 65 to 120 meters (36 to 65 fms.). Since
the general character of the sediments also changes, it cannot definitely
be stated that oxygen alone is the controlling factor.

Bottom Water Temperature Characteristics.

Surface water temperatures to a depth of 400 meters have been discussed
by RoDEN (1958) and Roden and Groves (1959). Using Roden and
Groves' data, plus unpublished values obtained from various recent
Scripps hydrographic cruises in the Gulf region, it was possible to con-
struct a bottom isotherm chart of water temperatures for the Gulf, ex-
clusive of shallow inshore areas (fig. 11). As can be seen from this figure,
there is an orderly progression from shore to the deepest portions of the
Gulf of from more than 14°C. to 2°C. in the deep southern sections. From
between San Lorenzo and Tiburon Islands, south to Puerto Vallarta, the
edge of the continental shelf is fairly well marked by bottom temperatures
of between 14' and 10° C. From shelf-edge to the bottom of the central
basins, temperatures gradually change to about 4°C. However, the south-
ernmost basin from Los Mochis south, and the upper end of the Middle
American Trench area have bottom water temperatures of 2°C. or less,
which are characteristic of the bottom water of the equatorial Pacific.

One exception to the rule of decreasing temperature with descending
depth is the deep channel between Angel de la Guarda and San Lorenzo
Islands and Baja California, and the moderately deep Tiburon Basin.
Here, as was demonstrated in the case of bottom oxygen values, temper-
atures are nearly uniform from surface to over 1500 meters, resulting from
the intense tidal mixing in this channel and basin. For instance, in Roden

38

118" 32* 116

Fig. 11. Bottom water-temperature isotherms, Gulf of California, based on several hundred
observations, taken at various seasons during a 20-year period.

39

and Groves (1959, p. 18) it can be seen that in the month of April, surface
water temperatures are at about 15°, while bottom temperatures at below
1,000 meters are still as high as 12°C. During the warmest month of August,
surface waters may be as high as 28°, but at 200 meters, temperatures are
down to 15°, and at 1,000 meters no lower than 12°C. These warm temper-
atures, found at such great depths, have a marked effect on the com-
position of the fauna in the bottom and on the sides of these channels and
in Tiburon basin. Vertical stratification of assemblages, as it occurs in the
central and southern Gulf corresponding to changing depths, disappears,
and many species usually found in 150 to 200 meters may also occur at
the bottom in depths of 1500 meters. This offers some proof that temper-
ature is at least one of the more important controlling factors in deter-
mining faunal distribution on the bottom, and that pressure alone is
apparently not too limiting a factor.

The inshore or shelf water temperatures have been discussed in detail
by Roden and Groves, but a brief description can be given here. A pro-
nounced seasonal variation has been observed in all portions of the Gulf,
but the variation in the northern region above the large islands is the most
extreme. In the vicinity of San Felipe and Puerto Pefiasco, the annual
range of water temperature in shallow water is about 16°C., from about
14° in the winter to over 3rC. in August. This extreme temperature range
possibly excludes many benthic animals, and in fact the south side of
Tiburon Island is the extreme northern end of the range for a large number
of invertebrate species (fig. 12). The summer temperatures are warm
enough to permit the existence of many Panamic or tropical forms, but
the cold temperatures are limiting to many species with a presumed low
tolerance to extreme change.

At Guaymas and in the shallow waters south of Tiburon Island, the
annual range is from nearly 18° to 31.5°C., or a range of 13.8°, still limiting
to many tropical forms. However, at Mazatlan water temperatures range
from only about 20° to 30°C., a difference of about 9° to 10°. The Mazatlan
area also seems to be the northern limit for a number of strictly tropical
species, as well as the extreme southern limit for many of the endemic
Gulf of California species. Fig. 12 illustrates the various geographical
limits of a number of the common, shallow-water Gulf of California
species as compared to annual range of surface water temperatures. Of the
253 species of invertebrates chosen to illustrate this point (those with at
least 5 living station occurrences), 8 species are found no further south
than the vicinity of Tiburon Island on the east side of the Gulf. Also,
34 more species are not found north of the Hermosillo-Tiburon region.

40

WEST SIDE, GULF

EAST SIDE, GULF

ApproN 23" N. tol.
CABO SAN LUCAS-
(205-29'C

DEEP CENTRAL

GULF *!""■""•'"-... pes^jco

(I«9-3I2*C1

40

NoHhcrn limir»

3S

Sourhern limits

0,30

>\

A

D«

^^ \

"20

\ ,'

&»

Y

5

0

A

\,

SAN
FELIPE

LOS

CONCEPTION
BAY

<

§i

110

100
90

/

A

Sourhem lim

'■

eo

/

\

/

70

\

d'°

\

/

^50

\

,'

fe«

\

/

0 30

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20

' \ /''^

°

-'

v^

~^

X

o o

i

1 '!

!

S3

Fig. 12. Zoogeographic breaks in faunal distribution in the Gulf of California, based on living
ranges of common invertebrate species, as revealed from distributional data from this study
only. Thickness of the bars is related to the number of species within each zoogeographic break.
The two small sets of graphs demonstrate the total number of species with northern and
southern limits at each temperature break on both sides of the Gulf.

There is a partial break in distributions at Los Mochis, where a major
headland exists, although the presence of a temperature barrier at this
point is not known. It is known, however, that the Los Mochis region
represents a transition from arid to sub-humid climate, as well as a change

41

in regional geology. About 100 species range no further north than Tiburon,
and 15 species are found only between Los Mochis and Tiburon. Twentyfive
species have northern limits at Los Mochis, which is also the southern
limit for 25 other species. The next major break in distribution is Mazatlan,
with 12 species having a northern limit and 49 species having southern
limits there. There is also an indication that San Bias may be an area with
slightly different temperature characteristics, since a number of species
have their northern limits at this point (Keen, 1958). It must be realized
that fig. 12 is based only on ranges of the species as found in this study
under variable sampling conditions. The ranges for many of these species,
as reported in Keen (1958), are quite different, but as it was not stated
whether they were taken alive throughout the reported range, these
data were not used. Since the sediments are radically different on this
portion of the shelf, no one factor can be considered decisive. At least
south of Mazatlan, shallow water bottom temperatures will seldom, if
ever, drop below 20° C, a temperature which is often considered the lower
limit for true tropical animals.

The temperature distribution on the shelf and along the coast of the
west side of the Gulf of California is not so well known, as there is a con-
spicuous lack of stations where data of this nature has been recorded.
One can assume that inshore water temperatures at San Felipe, ranging
between 16° and 17°C. between maximum and minimum, will roughly
correspond to those at Punta Peiiasco, and are perhaps a little lower in
the winter. At Los Angeles Bay and along the Ballenas Channel region, the
annual range of temperature is much less, and maximum temperatures are
far lower than on the opposite side of the Gulf. They vary from about
14° or 15° to around 28° or 29°C., and have an annual range of 15°C.
These temperatures are also limiting to a number of species. Both a smaller
number of Panamic or tropical and a larger number of California or warm-
temperate species of invertebrates have been reported there.

Water temperatures along the shores of the central portion of the Gulf
of California peninsula from San Lorenzo Island to La Paz range from
about 19° to 29° C, according to a cross-section shown in Roden and
Groves (1959, p. 21). The range between maximum and minimum water
temperature is less than at Los Angeles Bay (10°C.), but considerably
higher, thus permitting the existence of a much larger number of Panamic
species.

Temperature records exist for the La Paz region, which is situated in
protected waters, and therefore are probably not representative of true
conditions on the outer coast of the southern portion of Baja California.

42

Roden and Groves state that temperatures at La Paz average from 19.8°
to 21.1°C., with a range of 9.3"", which is quite similar to the temperature
distribution at Mazatlan, and typical of a true tropical environment.
Figures are also given for Cabo San Lucas, which is slightly warmer,
having only 8.5° C. difference between winter and summer. Cape San
Lucas seems to have the narrowest range of temperature in the Gulf,
being comparable to oceanic equatorial Pacific surface temperatures. This
may explain why a number of Indo-Pacific invertebrates and fish can be
found only in this region (Walker, 1960, and Rosenblatt, 1959). These
animals or their larvae must be transported by oceanic currents from the
central Pacific islands to this small cape where suitable ecological con-
ditions, consisting of a small coral reef and warm clear waters, can be found.
In many respects. Cape San Lucas has an environment similar to a tropical
Pacific island, and thus may be the closest habitat of this kind to be met
with along the coast of Middle America. The faunal breaks along the west
side of the Gulf (fig. 12) can also be closely correlated with various shallow
water temperature regimes and other physical barriers.

Salinity Distribution in the Gulf of California.

No independent study of the salinities in the Gulf was carried out by
this investigator. It was observed from earlier studies that salinity differ-
ences from one end of the Gulf to the other, and from surface to bottom,
were of such small magnitude that they were assumed to be relatively
unimportant in influencing the distribution of most benthic animals.
Roden and Groves (1959, p. 15) show a difference of only one part per
thousand salinity from winter to summer, and from Punta Peiiasco to
Mazatlan. The isohalines at 10 meters depth for April and August are
reproduced on figs. 13a and b. Likewise, from surface to 1800 meters
depth, salinity deviates from only 367oo to 34.6%o, a difference too small
to be of significance to most marine animals.

There are certain inshore regions of the Gulf of California, however,
which are characterized by salinity changes large enough to be significant
to animal distribution. These areas are the lagoons and bays along the east
coast of the Gulf from the Costa do Hermosillo to San Bias, Nayarit. The
salinities in these lagoons and estuaries are influenced both by prevailing
climate and by seasonal climatic changes. Those lagoons situated north
of Los Mochis in the arid to semi-arid Sonoran coastal climate, seldom
receive enough runoff or river discharge to make them brackish, but often
the extreme high summer temperatures and high evaporation rate may
bring about long-period hypersaline conditions (Nichols, 1962 and 1963).

43

Because of these adverse conditions, few benthic animals can live in these
lagoons permanently, and they are frequently barren of macro-invertebrate
life. Nichols (1962, 1963 and personal communication) has studied one of
these Sonoran lagoons (Laguna La Cruz) and states there was evidence
that oysters and mussels may have at one time been very abundant, but
are not living there now. Personal observations of Indian middens in the
vicinity of the same lagoon north of Guaymas revealed the existence of a
number of lagoonal or brackish-water mollusk species. These species may
have been living in the Sonoran lagoons during the supposed pluvial
period occurring about 900 to 1,000 years ago in the northern Gulf region
(HuBBS and Miller, 1948 and personal communication).

The lagoons from Rio Fuerte south to Mazatlan are still situated in a
semi-arid climate but receive considerably more fresh water from the
rivers, which are more or less permanent. These lagoons permit the ex-
istence of seasonal populations of shrimp and permanent beds of oysters,
but little is known of the other inhabitants. It is known, for instance,
(Fred B Phleger, personal communication) that the salinities in this
group of lagoons may fluctuate widely, being almost fresh during the brief
rainy seasons, and hypersaline during the peak of the dry season. The
exact range of salinities is at present unknown to this author.

A series of large lagoons south of Mazatlan to San Bias are very distinct
geologically (Curray, in van Andel in press) and hydrographically. They
are for the most part in the low salinity range, although the northern ones
may have high salinities in the summer. A permanent population of shrimp,
Corbula, oysters and Anadara clams live there, which are utilized for food.
These lagoons from the San Bias region to Manzanillo are true estuarine or
low-salinity lagoons, whose counterparts were studied along the humid por-
tion of the Texas-Louisiana coast (Parker, 1959). Rainfall and river dis-
charge are sufficient to maintain a permanent low salinity regime in at least
some portions of every lagoon. Unfortunately, no exact figures are available
to this author as to the range of physical factors, although they have been
studied in some detail by Fred B Phleger and Gifford Ewing (in
preparation). Personal collections of faunas from these lagoons were not
made, but a few forms were collected for the author by Joseph R. Curray
and Fred B Phleger.

General Circulation within the Gulf of California.

The circulation in the Gulf of California has been discussed by Roden
(1958, pp. 32-37), but a short discussion of the general characteristics must
be given here to supplement the survey of the general physical description

44

\Z ZX /

Fig. 13 a. Areal distribution of salinity ("/oo) at depths of 10 meters for April, 1957 (from Roden

and Groves, 1959).

45

^^ T

y

/

60 HAUTICAL MILES ,

Fig. 13b. Areal distribution of salinity C/oo) at depths of 10 meters for August, 1957 (from

RoDEN and Groves, 1959).

46

of the Gulf of California. According to Roden, the circulation in the Gulf
is somewhat complicated and not completely known. In the winter months,
the outflow of water is thought to occur at the surface, and inflow at greater
depths. In the summer, this situation is reversed.

During the winter months (December — March), the high salinity waters
in the northern Gulf are cooled, filling the northern basins and moving
southward along the coast of Baja California. This movement of water,
plus strong tidal currents through the narrows between the large central
islands attains speeds of several knots. This situation causes the turbulence
which, in turn, is responsible for the abnormally high bottom oxygen and
temperature values described previously for this region. According to
U.S. Hydrographic Office charts (1947), coastal surface currents move
south along the Baja California side of the Gulf in the winter months. In
July, water moves into the Gulf at the surface along the east side and
center of the Gulf, with some water moving in a southward direction close
to the southern portion of the Baja California peninsula. According to
Roden (1958), the monthly average speed of these currents in the southern
and central portions of the Gulf is between 5 cm. and 20 cm sec.

Except for the anomalous situation in the tidal channels between the
large islands in the Gulf, these surface currents probably have little effect
upon the adult sub-littoral benthic animals. They are important, however,
in influencing the planktonic larval transport of many benthic animals.
The fact that the currents moving into the Gulf from the south seem to
terminate in the vicinity of Tiburon Island, may account for the fact that
few truly Panamic species with planktonic larvae are found in the northern
Gulf above Tiburon Island. Although water does flow north through
Ballenas Channel, the colder surface water temperatures, due to turbulent
upwelling, may restrict the movement of Panamic species into the northern
Gulf on the west side. The fact that many moUusk and crustacean species
taken on the east side of the Gulf do not appear on the west side, and vice
versa, might also be explained by the fact that the currents on opposite
sides of the Gulf flow in opposite directions. The longshore currents on the
east side, with a prevailing movement to the north, also influence the
distribution of the fine sediments, so that clayey bottoms are generally
found to the north of the few permanent river mouths. Indirectly, then,
the currents influence the distribution of clay bottom dwellers in providing
their special niche in specific areas.

47

Description of the Macro-Invertebrate Assemblages and
Environments

The present sample coverage and available data is inadequate for a
thorough discussion of all of the possible assemblages that might exist
in the Gulf of California, but it is at least possible to describe the more
important ones and especially those that are likely to occur in the fossil
record. The number of ecological niches, both large and small, is very
great for such a relatively small region, particularly along the rocky,
dissected coast of the west side of the Gulf. The fine-grain carbonate mud
environments are the only ones completely missing from this region. There
are small patches of coral reefs (Squires, 1959), but they do not compare
in size with those of the Caribbean and Indo-Pacific regions. On the other
hand, with the exception of the fine-grain carbonate environments, almost
all other possible environments of deposition which have occurred during
the Tertiary history of the Americas can be found in the Gulf of California.
The polychaetes some of the Ophiuroids and Asteroids, Anthozoans,
Sponges and Bryozoans have not yet been identified; therefore, these
assemblage lists are incomplete, especially with regard to the smaller and
sometimes most abundant animals, which have served to characterize
communities in other regions.

I. The intertidal and shallow rocky shores assemblage.

The fauna of the intertidal rocky shore environment inhabits the major
portion of the shoreline of the Gulf of California and along the coast of
Middle America. It is also possibly the most easy to recognize, either
in situ or in older sediments. Many papers have been written on the
composition of the rocky intertidal fauna and flora of the world, partic-
ularly the series of papers by the Stephensons, too numerous to cite here,
and a review by Doty (1957). The majority of these papers have been
concerned with the intertidal zonation in temperate or boreal regions,
where attached algae play an important role in influencing the composition
of the fauna. Very few papers give a comprehensive idea of the composition
of the intertidal rocky shore fauna of the fantastically rich Gulf of Cali-
fornia region. Some idea of the diversity of mollusks to be found in this
habitat can be obtained in Steinbeck and Ricketts (1941), Keen (1958),
McLean (1961) and Dushane (1962). It would be impossible to list here
all of the animals known to occur in this environment, but at least the
most common ones found in this study and a few others known to be
abundant from other papers are given in Table II of the appendix.

48

The computor list of species common to stations occupied in this habitat
was very incomplete, and of little value in assessing the true nature of the
fauna living on rocky shores. Collecting in this environment was not at all
systematic, since this study was originally to be confined only to level
bottom areas. The species assigned to this environment with the greatest
significance by the computor were: the gastropods Nerita scabricosta,
Purpura patula pansa, Turbo fluctuosus, and Pyrene fuscata; and the
pelecypods, Barbatia reeveana, Isognomon chemnitziana, Ostrea conchophila,
Anomia adamas, and Cardita affinis californica. Anomia and Ostrea were
only found as dead shell within the samples, although this author observed
large numbers of them attached to the rocks. Actually, the above gastropod
species were observed to be very abundant in all rocky localities examined,
along with numerous chitons, patellas, neritids, littorines, and turbinids.
The four stations considered most indicative of this environm'ent, and the
portions of the shoreline inhabited by the rocky shores animals are shown
on fig. 14. So far, 53 living species of invertebrates have been identified
from the intertidal rocky shores environment, and another 18 species
known to live on rocky shores from the literature were also taken in the
vicinity of the rocks, but only as dead shell. A few of the typical mollusks
are figured on Plate I. Only mollusks are figured on these plates, since the
other invertebrates are still in the hands of the various specialists and
could not be photographed at the time this paper was being written.

McLean (1961), in his list of invertebrates from Los Angeles Bay, gives
105 species of mollusks which occur either on the rocks or in the sand
among the rocks (really two separate habitats). Dushane (1962) also
lists 145 species of mollusks living around the rocks in a small cove at
Puertocitos, somewhat south of San Felipe on the west side of the Gulf.
Many more species were reported by these authors than were found in the
present study. A much larger list of intertidal mollusks can also be gleaned
from Keen (1958). Since this study was originally proposed as a study of
level-bottom faunas, this environment is discussed only briefly in order
that paleontologists working on fossil deposits surrounding the Gulf of
California and along the Pacific coast of Central and South America may
have some frame of reference for separating out this assemblage from those
assemblages which are normally found on level bottom.

II. Intertidal sand beaches and sand flats to 10 meters.

The waters edge of the sand beaches and adjacent sand flats to depths
of about 10 meters are characterized by a fauna which closely resembles
that found on the sand beaches and in the nearshore Gulf of Mexico as

49

118' 32' US' 114' 34"

112*

^/ A- / /<x /

X

/

118*

30'

117*

; / fx

>

34*

^ S \ f "

/

110*

116"

Vii

/

32'

26'

" V 1 V

y

108*
30'

114"

- )l W

.y

/

24*

< € ■/' J_^

y^

\

28*

112*

> \f T

106*

22-

; 1

y

26-

"' *^

•i>

/

104*

20*

^ J

/

24-

18*

1

/
/

y

102*
22*

108*

C^^ Wm HOCKY COAST ^_;
^ SANO COAST ^

\

,s.

• COMPUTOR ANALYSIS STATIONS g. ;

60 NAUTICAL miles/
/\ /

20*

106' IS* 104'

102*

Fig. 14. Distribution of sandy and rocky areas along the coast of the Gulf of California. Station
locations for rocky shore localities bound together by matrix-associated species.

4 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

50

described by Parker (1956 and 1960). In extent, this environment and its
assemblage covers almost as much shoreline as the rocky shores, as shown
in fig. 14. One third to one half of all known mollusk species from the Gulf
of California have been reported from this environment, since the majority
of records are a result of collecting along sand beaches which are most
accessible from human habitation. It is difficult to ascertain from the
literature which species were found in the living state in this environment
alone. Thus the characteristic species, which are listed in Table II are
those from the present collection, with the exception of a special list
extracted from McLean (1961) given below.

As on the rocky shores, collecting along the sandy shores was also
somewhat haphazard, and most of the samples along the shore were taken
by hand. The subtidal portion of the environment, however, was sampled
mostly by grab samples (Table III, fig. 2a), i.e.: 3 orange peels, 5 Van
Veens, 1 dredge, 2 minidredges and 2 by diving. Because most of the hard-
shelled animals which may live to depths of 10 meters may also wash
onto the shore and become incorporated into sand beach deposits, no
distinction was drawn between the tidal and subtidal portions of this
environment. There is certainly a different group of animals living in the
deeper portions of this environment than right at the shoreline.

Only three species were assigned to a group of stations in this environ-
ment by the computor program, Cardita megastropha, Tivela byronensis
and Heterodonax bimaculatus, of which only Heterodonax can be considered
a characteristic species, the other two not even having been taken alive.
In a number of localities it was observed by the author that Heterodonax
could be scooped up by the handfuls by digging just below the sand surface
at the water's edge. The other two species, although not taken alive during
this study, are listed as typical nearshore sand bottom species by other
authors. The typical animals found at the water's edge, as observed by this
author are: Cerithium albonodosum, Bulla gouldiana, Heterodonax, nume-
rous species of Donax, Uca crenulata and Ocypode occidentalis. The other
species given in Table II are typical of the sub-tidal portions of this
environment. In the sub-tidal portions the most abundant living species
and also the most characteristic are : the gastropods, Strombus gracilior,
Oliva spicata, Olivella anazora; the pelecypods, Transanella puella, Mega-
pitaria squalida, and the most important Tellina felix; and the echinoid
Eucidaris thouarsi. The list of abundant, although not taken alive, species
on Table II for this environment is also given, since it is known that most
of these species have been recorded as living in this environment by others,
and can be considered useful index species for the paleontologist. Although
all species given in Table II occur in this environment, not all occur

51

together in the same geographic region. Most of them range along the
coast from the head of the Gulf to Panama, but a few are restricted to the
southern Gulf, or are not found north of Mazatlan.

There are many other species of invertebrates known from other col-
lections, which are more abundant on the sand beaches and on sand bottom
to depths of 10 meters, and are perhaps more typical of this environment
than those given in Table II. McLean (1961) lists two sand dollars,
Encope grandis L. Agassiz and Encope californica Verrill, as living on the
sand flats at Los Angeles Bay, and although Encope tests were frequently
noticed on the beaches, no living specimens were collected along the beach
during this present study. Dushane (1962) also gave a large list of mullusks
found on sand or sand-mud bottom at the same depths near Puertocitos.
She included at least 112 moUusk species which definitely live in this
environment. The mollusks found alive on the sand flats to depths of
four or five meters in Los Angeles Bay by McLean are given in a list below
in order to illustrate the diversity of species from one locality in one
environment.

Prosobranchs
Calliostoma eximum
Neritina luteofasciata^
Balcis cf. rutila
Cerithium sculptum
Cerithium albonodosa^
Cerithidea mazatlanica
Natica chemnitzi
Polinices bifasciatus
Polinices uber
Polinices reclusianus
Strombus gracilior^
Strombus granulatus^
Hexaplex erythrostomus
Nassarius iodes
Nassarius moestus
Nassarius tiarula^
Oliva spicata^
Olivella dama
Cancellaria cassidiformis
Conus ximines
Terebra variegata

Tectibranchs
Bulla gouldiana^

Haminoea angelensis
Haminoea strongi

Pulmonates
Melampus olivaceous

Lamellibranchs
Anadara multicostata
Anadara cepoides
Glycymeris gigantea
Glycymeris maculata
Glycymeris multicostata
Pinna rugosa
Atrina tuberculosa
Trachycardium consors
Trachycardium panamense
Trigoniocardia granulifera
Laevicardium elenense
Laevicardium elenense apicinum
Pilar newcombianus
Megapitaria squalida^
Dosinia ponderosa
Protothaca grata
Heterodonax bimaculatus^
Lyonsia gouldii

^) Species also taken alive in the sand beach and sand flat environment in the present
study.
4*

52

The majority of the above species were also collected by the present
author on sand beaches, although not found in the living state. Many of
the species, however, were taken alive at greater depths, and may be
more abundant in the deeper assemblages. A much larger list can be
obtained from Keen (1958), although it is nearly impossible to tell which
mollusks of Keen's list are confined to these depths alive. A few of the
typical mollusks are given on Plate II.

III. Low-salinity lagoon and mangrove assemblage.

This environment was not studied in detail along the Pacific coast of
Mexico, although a few small hand collections were taken by this author
(Table III) and specimens were collected by other members of Scripps
expeditions from various brackish lagoons along the Mexican coast. This
discussion is confined to mollusks, but it is well known that several species
of commercially important shrimp and crabs occur in large numbers
within the lagoons between Mazatlan and Panama. Little information
is available as to the other kinds of invertebrates inhabiting the lagoons
and mangrove swamps. Inlets into the lagoons south of Mazatlan are
small, restricted, and are apparently closed rather frequently. For this
reason, few strictly marine animals will be able to survive in the lagoons,
and salinities are seldom high enough to support a wholly marine fauna.
A list of the typical mollusks found in this environment, as selected from
Keen (1958) is given below. Certain species in this list are quite important
as food, especially Anadara tuberculosa, Ostrea columbiensis and Ostrea
corteziensis. A few of these low-salinity mollusks are figured on Plate III
and all are illustrated in Keen (1958).

Prosobranchs
Neritina luteofasciata
Neritina latissima
Cerithidea mazatlanica^
Cerithidea montagnei^
Littoridina, sp.

Tectibranchs
Bulla gouldiana^

Pulmonates
Melampus olivaceous^
Ellobium stagnalis

Lamellibranchs
Anadara tuberculosa^
Mytella falcata
Ostrea columbiensis
Ostrea corteziensis^
Polymesoda mexicana^
Polymesoda (7 more species known)
Cyrenoida panamensis
Mytilopsis adamsi
Rangia mendica^
Corbula inflata

^) Collected as a part of this study.

53

IV. Nearshore, sand and sand-mud, 1 1-26 meter assemblage.

This is by far the most prolific assemblage in species and numbers of
individuals of invertebrates in the Gulf of California, so far as the present
sampling is concerned. In accordance with Liebig's "Law of the Minimum",
as restated in Parker (1959), there is good reason for the great diversity
and size of the population, since the ecological conditions are optimum
for most marine species. Salinities are constant and at normal oceanic
values, and water temperatures have a much smaller annual range than in
the inshore environments. The water is also relatively quiet at these depths
which are below wave base for the rather small-sized waves of the Gulf
of California. Sediments therefore range from sand to sand-mud and
mud-sand, or in Shepard's (1954) terminology, sand, silty sands, clayey
sands, sandy silts and sand-silt-clay. These sediments are less well-sorted
than those in the previous environments, permitting greater amounts of
organic detritus to accumulate, thus making it possible to support a
larger population of deposit-feeding animals. These, then, are optimum
conditions for the existence of most marine invertebrates. A total of 258
species (living and dead) from all stations, and 172 living species from the
27 characteristic stations were identified from this environment. A com-
parison of the number of species taken at all depth ranges is given in fig. 15.

The separation between the northern and southern Gulf is relatively
distinct in this environment. The contingency matrix provided the basis
for two separate assemblages, both on sand bottom and in from 1 1 to
26 meters depth, one in the Tiburon region and the other south of Mazatlan.
There is a possibility that separate groupings of animals resulted because
of different kinds of sampling gear. The majority of samples in the northern
region were taken by shell dredge (10 shell dredges, 2 Van Veens, 1/15 m^
and 2 3-meter otter trawls), while in the southern region grab samples
outnumber dredges and trawls (4 Petersen grabs, 1/10 m^, 3 Van Veen,
1/20 m^, 2 orange peels, 1/15 m- grabs, 3 3-meter otter trawls, and 1 mini-
dredge) as shown on Table III. Regardless of the difference in balance of
collecting devices between the two areas, at least some dredging and grab
sampling was carried out in both places. Examination of the list of living
animals only from the northern and southern nearshore shelf region
(Table II) shows roughly the same size and kinds of animals from the two
regions, even though the species were often different within the same
subgenus. For instance, 25 species were taken in common between the two
areas, or slightly less than one quarter of the total of northern species and
slightly less than half of the total of southern species. There were two more
species of corals, almost twice as many species of prosobranchs and

54

DEPTH
NUMBER

STATIO^B

PER

DEPTH

300
290
280

i'ho

260
2 50
240
230
220
210
200

~"

\

. \

_ :t::::m :::::::::::

1/1

li -4 • • NUMBER OF SPECIES 2

' L »--- NUMBER OF STATIONS

J

1

i ^ —

_.:::::_r \ .

/ „ ^ 1 ^L.-—

I J^h' -1- -1 -

Vtu l-i-—

'^T \t"::i:::-i.A l-l—

' T I 1 1

1 T y 1

"" 'r"":"""T Z-" :::::::i::t:::]^:::" J

:._ i. _„v 1 '_<u

"" T Tn .- J L_ "--ii-Jr

— j:rir>' > "./ i^.i.i}^^

^ ^ ,y s:t^^__,__.__

T-rn L ; I i^^ \

;

]r"J4rsr""' ""::iIhU^Jl

/\

i ir " Miv^.^"^

A 5

t SzAtUVfti

4

^ \,LVa

^/i \

DEPTHS IN FATHOMS

Fig. 15. Graphs of the number of species occurring at various increments of depths from shore

to abyss, as compared to the number of stations occupied in the same depths. Species totals

include both living and dead occurrences.

crustaceans, but six times as many echinoid species in the northern than
the southern region. However, there were the same number of lamelli-
branch species, indicating that the catch effort for infauna was about the
same, but that the excess shell dredging in the northern region produced
more eplfaunal or motile forms than the grab sampling in the south. With

55

the slight information available from the present physical data, it would
seem that extremes of water temperature play an important part in
producing a somewhat different infauna in the southern than in the
northern part of this environment. As shown in fig. 12, inshore water
temperatures range from 15^ to 30° C. in the Tiburon region, while south
of Mazatlan, the range is much less and higher (22° to 30° C). This is
somewhat substantiated in that if one compares the two lists in Table II,
it can be seen that there is usually a replacement of species within the
same genus between the two areas, and that if one looks at the published
ranges of these species, the southern species are those which have not been
previously cited in the northern Gulf. Sediments were also somewhat
finer and less well-sorted in the southern region. One of the reasons so few
grab samples were taken in the Tiburon region, was that none of these
sampling devices would work in the hard sand and shell-sand bottom. The
shell dredge was the only device that would dig down into the bottom, and
in fact was frequently the only source of sediment samples for the geo-
logists, as their coring devices would not operate either in the hard bottom.
The Tiburon region is also affected by upwelling (fig. 10), while no up-
welling takes place in the San Bias region. This factor alone creates not
only differing water temperatures, but also varying food supply.

Actually, the Tiburon region in depths of four to thirty meters is very
complex in patterns of invertebrate distribution and no different from any
other marine bottom in this respect. Five different groupings of animals
resulted from the contingency matrix, each with a slightly different set of
stations in common (fig. 16). Since both living and dead occurrences were
used to establish the stations groupings as shown in fig. 16, these patterns
may not be very significant. They are given, primarily to show the com-
plexity of distributions which may result from such a program. Table IV
gives the list of the species which comprised the index groups from the
computer program, listed as to their importance and number of stations
common to each within its group. The tabulation of the known physical
factors for each group is also shown.

Since the above computor analysis produced a somewhat confused and
probably false impression of the true assemblage (since both living and
dead records were used), a more reliable assemblage was devised from a
combination of all of the index groups, using the somewhat more subjective
method of analysis mentioned in the discussion of methods. All species
which were involved in the matrix analysis were listed and compared as
to common station occurrence and abundance only as living records. It
was then possible to select the stations where the greatest number of these

56

26"«' ll?30'

2i-iCf imo'

DEPTH CONTOURS

Fig. 16. Areal distribution of "index groups" of assemblages in the northern nearshore shelf
environment. Station composition and range of ecological factors for each group can be found
in Table III. The boundaries of the groups are somewhat subjective, agreeing in general with
the bathymetry and sedimentary patterns. Station numbers shown are those with highest
affinity, although others were involved in determining the boundaries, but were much less

important.

common species were found, and also those species which were either
unique to or had the greatest percentage of occurrence within these sta-
tions. A map of the station locations resulting from this analysis is shown
on fig. 17.

57

Fig. 17. Areal distribution of composite group of stations characterizing the nearshore shelf

environment in the northeastern Gulf region. These stations had the greatest number of common

occurrences of species from all index groups.

In terms of strict abundance (as a qualitative term [see Thorson, 1957,
p. 474]) within the nine stations considered characteristic of the 11 to
26 meter nearshore shelf environment in the northern Gulf, the following
species can be considered the most important, and may actually form the
basis for a community, when more systematic sampling is carried out.

58

Many of the really abundant forms are epifaunal in nature (actually
attached to objects on the bottom), which can be attributed to the nature
of the bottom, being in many places a shell-sand, with large quantities of
dead shell furnishing a place for attachment. These animals, Heterocyathus,
and two species of Astrangia (corals), the immense numbers of Calyp-
traeidae {Calyptraea, Crucibulum and Crepidula), the equally numerous
barnacles and pagurids living in dead gastropod shells, are dominant in a
sense, but cannot be considered part of the infaunal level-bottom com-
munity. The most abundant infaunal animals were the prosobranchs,

Table IV.

Species

Index Group Numbers

J

64

74

Gastropods

Crepidula arenata

Crepidula excavata

Polinices intemerata

Polinices reclusianus

Strombus gracilior (Index species grp. 64). . .

Hexaplex erythrostomus

Distorsio decussatus

Nassarius versicolor

Strombina gibberula

Olivella fletcherae

Terebra specillata

Acteocina angustior

Lameilibranchs

Nuculana elenensis

Barbatia alternata

Anadara obesa

Lioberus salvadoricus

Chlamys circularis (Index species grp. 2) . . . .

Lucina prolongata

Ciena mexicana

Laevicardium elatum

Laevicardium elenense (Index species grp. 7) .

Trachycardium panamense

Trigoniocardia biangulala

Megapilaria squalida

Dosinia dunkeri

Chione mariae

Tellina amianta

Tellina inaequistriata

Macoma siliqua

Semele guaymasensis

Donax gracilis (Index species grp. 74)

Ensis californica (Index species grp. 3)

Crustaceans
Portumts pichelinqui

{continued)

59

Table IV (continued).

I

ndex G

roup Numbers

Physical Factors

2

3

7

64

74

Station Depth in Temp. Oxygen Sediment

Numbers fathoms in°C. in ml/1. type

X

24 13 16 2.5 Sand

114 4 30 4 Sand

X

163 1 20 4 Sand

X

172 7 20 3 Shell sand

X

175 14 13 1.2 Mud sand

X

179 1 14 3 Sand

X

181 9 18 3 Sand

X

X

184 9 14 3 Sand

X

X

X

185 31 13 2.4 Sand

X

X

190 7 20 3 Sand

X

191 14 15 3 Mud sand

X

194 7 20 3 Mud sand

X

195 12 18 3 Mud sand

X

196 13 16 3 Sand

X

X

X

X

208 7 19 2.6 Sand

X

212 31 13 2.4 Sand

10.6

19

16.6

7.4

Average Environmental Depth in fathoms:

9.4

Conditions Temp, in °C.:

17

14.3

14

19.2

18

Oxygen in ml/1.:

2.6

2.8

2.7

3.2

3.2

Sediment type:

Mud 3/5 Sand 6/7 Sand 3/4 Sand 6/7 Sand

Table V.

Species

"/„ of Occurrences

in Computer

Stations, alive

o/o of Total live

Occurrences in

Whole Gulf

Index

Laevicardium elatum

Hexaplex erythrostomus

Donax gracilis

Ensis californicus

88

44

44

44

33

33

66

66

55

55

44

33

33

60

Lesser

Importance,

Living

44

20

44

71
100
100
100
100
100
60
50
60
57
66
75
75
40

50
60
40

80
72

72
72

Strombus gracilior

Tellina tabogensis

66
66

Polinices reclusianus

Trachycardium panamense

Olivella fletcherae

63
58
58

Crepidula excavata

Terebra specillata

Lioberus salvidoricus

56

55
54

Anadara obesa

Laevicardium elenense

Trigoniocardia granifera

Crepidula arenata

54
50

47
43

Nassarius versicolor

42

60

Polinices reclusianus, Strombus gracilior^ Cantharus pallidas, Nassarius
versicolor, Oliva incrassata, Olivella fletcherae, Hexaplex erythrostomus,
Mitra hindsii, Pleuroliria picta, Terebra specillata and Terebra variegata;
the lamellibranchs, Nuculana elenensis, Nuculana fastigata, Anadara
obesa, Chlamys circularis, Trachycardium panamense, Laevicardium elatum,
Laevicardium elenense, Megapitaria squalida, Chione mariae, Tellina tabo-
gensis, Macoma siliqua, Donax gracilis, Ensis californicus and Lyonsia
gouldii; the echinoids, Lovenia cordiformis and Moira clothe; and the
ophiuroid, Amphiodia occidentalis (Lyman). The family of mollusks with
the most number of individuals was certainly the Cardiidae, followed by
Veneridae and Turridae. Few polychaetes were noted and so far the only
ophiuroids and asteroids identified are: Amphiodia occidentalis and
Astropecton californicus.

As mentioned previously, the 11 to 26 meter sand bottom assemblage
extends the length of the Gulf and probably to Ecuador, but the individual
species composition changes somewhat to the south. Some of the differences
between the north and south portions of this environment can certainly be
attributed to differing sampling devices. This is especially true with respect
to the decapod crustaceans, which were quite abundant in the northern re-
gion, collected mostly by dredge, and relatively uncommon in the southern
region collected by grab samplers. On the other hand, the most common
infaunal species were either of the same species or of the same genus in
both regions, illustrating the uniformity of the assemblage along the entire
coast. The contingency matrix did provide a basis for selecting stations
representative for the southern nearshore shelf by finding several groups
of closely associated species belonging to the stations shown on fig. 18.
Sampling devices used for those stations are on Table III. A list of the
living invertebrates from the 13 stations on fig. 18 is given in Table II,
which when compared with the list of species for the Tiburon region also
in Table II, gives an idea of both the similarity and uniqueness of the two
faunas. A number of typical mollusks from this environment (both north
and south) are illustrated on Plate IV, while others can be seen in Keen
(1958) or Olsson (1961).

V. Intermediate shelf, 27 to 65 meters.

The contingency matrix provided a very distinct set of stations, which
served as a basis for examination of the faunal associations in these depths.
Unfortunately, the northern portion of the intermediate shelf was sampled
primarily by shell dredges with a one meter opening (Table III), while
the southern part was sampled mostly by 12 and 3-meter wide otter trawls

61

Fig. 18. Distribution of stations from which the distinct matrix group of animals characteristic
of the nearshore shelf in the southern Gulf were taken.

62

(Table III). No grab samples were taken in any part of this environment,
which must account for the relative scarcity of infaunal species as com-
pared to regions sampled elsewhere in the Gulf where grab samplers were
occassionally used. As can be seen in the lists of living animals from both
the northern and southern portions (Table II), crustacean and prosobranch
species far outnumber any other kind of organisms, and these kinds of
animals are most likely to be taken by dredges and trawls.

Even though no grab samples were taken, which might serve to show
a true difference between nearshore and intermediate shelf faunas, there
is no doubt that the intermediate shelf assemblage is a distinct one, with
depth boundaries at about 27 to 65 meters. The fact that decapod cru-
staceans proved to be important index species in providing a characteristic
set of stations for this environment, both in the north and the south,
lends more support to this idea, since these animals are motile, and would
be expected to range over several communities or environments, unless
the physical boundaries might be fairly sharp. The contingency matrix
indicated a close association between 18 invertebrate species in the Tiburon
region in depths from 25 to 76 meters. The distribution of these stations
and three other closely associated stations is shown in fig. 19. As shown
in Table III, these stations were taken by 7 shell dredges, 4, 3-meter
otter trawls and 2 rock dredges. Although the list of associated species, as
given by the matrix is primarily an epifaunal one, and the mollusks are
both living and dead species, it is given here for reference. The complete
list of invertebrates identified so far from the Tiburon intermediate shelf
region is given in Table II.

Species D.gr..o/
'^ Association

Degree of
Association

Gastropods

Solecurtus guaymasensi.

Polinices uber (dead)

11

(dead)

16

Fusinus dupettithouarsi

12

Plicatula inezana

18

Natica grayi

15

Crustaceans

Lamellibranchs

Euprognatha bifida

Nemocardium pazianum

6

(Index Species)

1

Chione mariae

8

Mesorhea belli

2

Diplodonta subquadrata

Randallia americana

3

(dead)

9

Collodes tenuirostris

4

Macoma siliqua

13

Pagurus gladius

5

Cyclopecten pernomus

Cancer amphioetus

7

(dead)

14

Paradasygius depressus

10

Cymopolia zonata

14

63

Most of the characteristic living species are listed in Table II, but the

following species can be considered the most abundant infaunal inver-
tebrates :

Prosobranchiata Crassatella gibbosa

Solariella triplostephanus Nemocardium pazianum

Natica grayi Chione mariae

Murex recurvirostris Macoma siliqua

Fusin us dupettithouarsi Trigon iocardia gran if era
Pleuroliria albicarinata

Echinoidea
Clypeasier europacificus

Asteroidea
Luidia Columbia Liitken

Lamellibranchiata Ophioroidea

Anadara nux Amphigyptis perplexa

A number of the species from these 13 stations as given on Table II
were also taken in shallower water and a few were found in deeper waters.
All stations were taken on sand bottom in an area where bottom temper-
atures range between 30° and H'^C. and the waters are well-oxygenated.
As an assemblage, there is a considerable difference between this one and
the one inshore of it, in that there was an enormous number of mollusk
species found only as dead shell, and not usually found living in these
depths elsewhere along the coast. Most of these species normally live in
depths of from 1 to 30 meters. A list of them can be compiled from Table I
by noting all species in the complete list which were taken from the 13
stations shown on fig. 19. These dead, but shallower shells, are important
to the paleontologist, however, in that they are part of an assemblage
which will eventually become buried and form a distinct fossil deposit
indicative of a transgressive sea. It is presumed (and somewhat sub-
stantiated by carbon- 14 dates) that the sand deposits in which these shells
are found have resulted from lowered sea level during the early part of the
Holocene. The shells of animals which once lived close to shore became
mixed with deeper species as the sea level rose, and the shoreline moved
inwards. It is known that strand line deposits resulting from lowered sea
level at around 7,000 to 1 1 ,000 years ago occur at depths of from about
40 to 80 meters throughout the world (Curray, 1960, 1962). Figs. 20a
and b show the distribution of two of the typical decapods found in this
environment, Cancer amphioetus and Randallia americana. The distribution
of two mollusks, the gastropod, Solariella triplostephanus, and the pele-
cypod, Trigoniocardia biangulata are shown in figs. 21a and b. The distri-

64

O

•<9o

56

■^ MATRIX STATIONS
INDEX GROUP 6

• COMPUTOR ASSOCIATED
STATIONS

^

jL

Fig. 19. Areal distribution of the northern Gulf, intermediate shelf environment, based on

stations brought into close association by matrix-associated species, especially index group

number 6 {Euprognatha bifida).

butional boundaries of these species, it can be seen, correspond closely
to the boundaries of the environment, fig. 19. Many other species of
invertebrates have a similar distributional pattern in this region, even
though sample coverage was relatively dense from shore to 200 meters
(fig. 2b), which is an additional proof that a distinct assemblage and

65

probably community exists in the area circumscribed by the 13 stations
in fig. 19.

This same environment probably continues uninterrupted along the
coast to at least Panama, but samples were taken at these depths in
sufficient numbers only south of Los Mochis to San Bias. A similar assem-
blage was also devised in which about one third of the species was taken
in common to the two sections. There were, however, a number of inverte-
brate species taken in the southern intermediate shelf region which were
not taken in the north, and these served to separate the areas by means
of the contingency matrix. As with the nearshore shelf, temperature seems
to play a part in creating different faunas in the north and south, since
many genera have species only found in the north and others only in the
south. The greatest difference between the two assemblages may, however,
be a result of the difference in sampling. Certainly the large trawls were
able to capture more of the large motile decapods and large prosobranchs.
These two groups were twice as abundant in the southern region where
trawls were used, than in the Tiburon region where they were only used
four times. The species most frequently occurring at the seven stations
which proved by preliminary computor analysis to be distinct are listed
in Table VI. The seven typical stations were taken on silty clay and ranged
in depths from 36 to 75 meters, as shown on fig. 22. In order to substantiate
the importance of the animals in Table VI for this environment, the same
system of computed indeces of uniqueness was computed as was for
Table V. It can be seen immediately that no infaunal species (unless you
consider the prosobranchs as living in the bottom) figured in the computor
analysis. What is significant, however, is that the species in Table VI are
very restricted in their distribution, even though they are capable of much
greater mobility than the other invertebrates.

A number of other stations were also occupied in the southern portion
of the intermediate shelf. Most of these stations contained the animals
listed in Table VI, but not in such a close association. The seven matrix-
associated stations constitute a nucleus or center for the whole assemblage,
while the others are on the periphery, and have a more heterogenous group
of animals. These 12 stations are shown on fig. 22. A list of the living
species collected from all 12 of these southern stations is given in Table II.
The most abundant infaunal species on sand bottom off San Bias were:
the prosobranchs, Calliostoma bonita, Astele rema, Architectonica placen-
talis, Natica broderipiana, Natica colima, Polinices uber, Distorsio decussa-
tus, Bursa nana, Murex recurvirostris, Hexaplex brassica, Coralliophila
hindsii, Cantharus capitaneus, Mitra erythrogramma, Knefastia walkeri,

5 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

66

Fig. 20a. Distribution of the decapod crab, Cancer amphioetus, confined to the northern Gulf,
intermediate shelf region. Number of specimens at each station circled.

Clavus roseolus, Hindsiclava andromeda, and Pleuroliria picta; the sca-
phopod, Dentalium oerstedii; and the lamellibranchs, Nuculana morella,
Glycymeris tessellata, Chlamys circularis, Cardita spurca beebei, Trachy-
cardium belcheri, Lophocardium cummingii, Tellina pristophora, and
Semele paziana. The abundant and perhaps characteristic species of

67

Fig. 20b. Distribution of the decapod crab, Randallia americana, indicative of the northern
Gulf, intermediate shelf region. Number of specimens at each station circled.

infauna on the clayey bottoms of the southern intermediate shelf are: the
gastropods, Architectonica nobilis, Natica elenae, Distorsio constrictus,
Bursa nana, Harpa crenata, Hormospira maculosa, Conus recurvus, and
Conus scalaris; the scaphopod, Dentalium oerstedii; and the lamellibranchs,
Noetia delgada, Glycymeris tesselata, Chlamys circularis, Plicatula inezana,

68

118* 32^ M^

Fig. 21a. Distribution of the gastropod, Solariella triplostephanus, indicative of the northern
Gulf, intermediate shelf region. Number of specimens encircled.

69

Fig. 21b. Distribution of the pelecypod, Trigoniocardia biangulata, characteristic of the

intermediate shelf in the central portion of the Gulf, although occassionally found in the

southern Gulf. Number of specimens also given.

70

II

}• 32' 116*

II4' 34'

II2*

/

/> /

/x / X

/

US'

j

JO-

\

V ,.

%

>

34'

1I7*

/

(/

1- \~^

/

110'

28*

lis-

/

f J ]i

J <-

\

32"

\

"^.

/

26*

\

1 1

^

y-

108'
30'

114'

■\

y^ r

/

24*

II2"
22*

<
>

/

\ H^

I54(i»\\.,

issXA jV,

151 •\F'...
I50l»'tej_

87/ |\.

y^

/

ag-
ios'

26-

\

94,95 \[|||)|.

J>

/

104*

20*

no*

/

l59/|||)r

/

24*

18'

\

<^COIIPUTOII AS90CI1TED

,™.(

7

102*
22*

I08'

<

C^AFFILIATEO STATIONS
• CLAt BOTTOM
®SANO BOTTOM

\

/
/

\

Y-

60 NAUTICAL MILES

16'

y

\y /\

/ 4

/\

/

20*

106' 16*

104"

102'

Fig. 22. Location of computor affiliated stations on sand and clay bottom upon which the
southern Gulf, intermediate shelf assemblage is based.

71

Table VI.

Species

"/o of Occurrences

at Computor

Stations

«/o of Total

Occurrences of

Species

within Gulf

Index

Crustaceans
Iliacantha huncocki

86

71
71
71

71
86
86
57
43
43
43

100
100

57
57
86
43

57
71

66
71
71
62
62
38
27
44
60
60
43

86
53
66
50
17
60
44
26

76

71

Persephone townsendi

Stenorhynchus debilis

Medaeus lobipes

Dardanus sinistripes

Pyromaia tuberculata

Paradysgius depressus

Randallia bulligera

Leilolambrus punctatissimua

Hepatus kossmani

Gastropods
Distorsio decussatus

71
66
66
62
57
51
51
51
43

93

Cantharus capitaneus

76

Calliostoma bonita

61

Architedonica nobilis

Crucibulum spinosum

Hexaplex brassica

Strombina fusinoidea (mostly dead) ....
Hormospira maculosa

53
51
51
50

48

Anodontia edentuloides, Trachycardium belcher i, Pilar calharius, Chione
mariae and Semele paziana.

A comparison was made between the occurrences of the species from the
southern intermediate shelf on sand or mud and as to whether they were
also found in the northern portion of this environment. Of the 128 species
of invertebrates found alive at the 1 1 stations, 40 species were common to
both sand and silty clay, and 16 of these also occurred in the north on
both sediments. Only 28 species were restricted to clay bottom in the
south, of which three were also found on sand in the north. On the other
hand, 57 species were found only on sand in the south (two stations),
eight of which were also found on sand in the north. All of the species
(living and dead) from the southern intermediate shelf can be found in
Table I. The distribution maps of the two southern crustaceans, Iliacantha
hancocki and Portunus acuminatus are shown on figs. 23a and b, while
the distribution of two gastropods, Bursa nana and Cantharus capitaneus
is shown on figs. 24a and b. The more common mollusks are figured
on Plate V.

72

Fig. 23a. Distribution and abundance of the decapod, Iliacantha hancocki, indicative of the
southern Gulf, intermediate shelf. Number of specimens for each station circled.

73

118* 32' 116*

114*

34-

112-
/

f

r^

>

{(

}^

/

-f jk

h ^

\

-;,

/

"■ % / *

1

m4

V

^ /I

\

/

^^v

/

\ L-^

-^

/

^

f?

u

/

f'

/

/

r^

■\^

1

y

<

V

/

\

LIVE-<|)

\

60 NAUTICAL MILES /

/ \/ /\

/ xX.

/\

/ ^

Fig. 23 b. Distribution and abundance of the decapod crab, Portunus acuminatus, confined to
the southern Gulf, intermediate shelf.

74

I14' 3«* II2*

7 T^r^v ^^ T

Fig. 24a. Distribution and abundance of the gastropod, Bursa nana, confined to the southern
Gulf, intermediate shelf region.

75

114* 34* 112*

Fig. 24b. Distribution and abundance of the highly characteristic gastropod, Cantharus
capitaneous, in the southern Gulf, intermediate shelf environment.

76

VI. Outer shelf, 66 to 120 meters, clay bottom, southern Gulf.
A portion of the outer shelf environment in the Gulf of California from

Los Mochis to just south of Mazatlan was verified by the contingency
matrix as being a distinct region. Six stations proved to be closely associ-
ated by five commonly occurring species, which were abundant enough in
numbers per station to identify the environment. The number of species
seem to decrease at these greater depths and especially in the matrix-desig-
nated region which is based on eight stations taken in a silty clay bottom
(fig. 25). The eight stations were sampled by six kinds of devices (Table III
and fig. 2a), yet each device produced essentially the same species attesting
to the uniformity of the assemblage. The devices used were: one orange
peel grab, two shell dredges, two 12-meter and one 3-meter otter trawls,
one rock dredge and one box dredge. The five associated species were:
a polychaete, Protula siiperba, two gastropods, Conus arcuatus and Cruci-
bulum, sp. (allied to C. striatum of the Atlantic), and two lamellibranchs,
Chione kellettii and Anadara mazatlanica.

A complete list of the living species (with the most abundant in number
starred) from the outer shelf clay bottom environment can be found in
Table II of the appendix, while all species living and dead from these
stations can be ascertained from a study of Table I. Two of the outer
shelf stations in the southern Gulf were taken on sand bottom, but only
two species (both epifaunal in nature) from these stations were also found
on clay bottom. The more important mollusks are illustrated on Plate VI.

VII. Outer shelf, 66 to 126 meters, sand bottom, northern Gulf.
All stations in depths of from 66 to 126 meters from just south of

Tiburon to Punta Peiiasco in the northern Gulf were taken on sand
bottom. This assemblage was completely different from the one found on
clay bottom in similar depths to the south. These stations (fig. 25) occurred
on what appears to be a residual sand bottom resulting from eustatically
lowered sea level, since nearly every station had a large number of dead
mollusk shells of species usually found living close to shore. A total of
93 living species of invertebrates, mostly epifaunal, were collected from
18 stations, giving an average of only five species per station. Owing to
the heterogeneous composition of the 18 stations on sand bottom in the
north, no closely associated group of species resulted from the contingency
matrix. Only two species of invertebrates occurred at enough stations in
this environment to be considered abundant (in the sense used by Re-
mane, 1940): the echinoid, Clypeaster eiiropacificus and the pelecypod,

77

lie* 32

Fig. 25. Location of matrix-associated stations in both the northern Gulf, sand bottom and
southern Gulf clay bottom environments on the outer shelf.

78

Lucinoma annulata, which are also found in deeper waters in the northern
Gulf. A large number of pelecypods, found as dead shells, were con-
sistently found in these and only these stations, but because of the pre-
sence of so many dead shallow-water species, one cannot be certain that
they lived at these depths. The most interesting aspect of this assemblage
was the large number of living gastropod and crustacean species. Many
of these species also occurred on inshore sand bottom to depths of less
than 20 meters. Apparently, the nature of the bottom is more important
than depth in the northern Gulf, so far as limiting the distribution of the
more mobile invertebrates is concerned. One likely reason for depth being
non-restrictive is that due to intense tidal action, the waters are thoroughly
mixed from top to bottom. Although almost half of the samples were
collected by shell dredge, five other devices were used (Table III), which
may have also contributed to the heterogeneity of the assemblage. These
samples were: seven shell dredges, one 10-meter and three 3-meter otter
trawls, five rock dredges, one orange peel grab, and one 1/10 m^ Peter-
sen grab.

All invertebrates taken in the northern Gulf outer shelf environment,
living and dead, can be determined from Table I, while living species only,
with the most abundant forms starred are given in Table II in the appendix.
A few of the common moUusks are figured on Plate VI.

VIII. Northern Gulf basins and troughs, 230 to 1,500 meters.

Owing to the peculiar temperature and sediment conditions in this deep
portion of the northern Gulf of California, this environment may well be
unique in the world today. The great tidal exchange through these basins
and channels create virtually uniform temperature, salinity and oxygen
conditions from about 30 to 50 meters close to the surface down to the
bottom at 1,500 meters. This turbulence plus the geological background
of the areas created an almost uniform sand to gravel bottom in all depths
(fig. 7). Since two very important ecological factors (water temperature
and sediment size) which are apt to bring about vertical stratification of
fauna are eliminated, it is interesting to see what effect, if any, the in-
fluence of pressure has had on the composition of the fauna in the deeper
portions.

The species found in this environment must be separated into two parts,
one composed of the living species and another which is composed mostly
of shell remains. Normally, dead shells would not be considered too
important, but in this instance it is interesting enough to be dealt with

79

separately. First of all, only 34 living species of invertebrate were taken,
although 19 stations were occupied (fig. 26). The sampling of this environ-
ment was based on six rock dredges, five piston cores (10 cm. diameter),
two gravity cores (4 cm. diameter), two box dredges, two shell dredges,
one deep diving dredge and one orange peel grab. The living animals were
taken by the various dredges, while the unusual shell remains were found
in the cores and orange peel. Except for the deep diving dredge (really
a trawl), no large-opening samples were taken, which accounts for the lack
of large crustaceans which are so important in the other Gulf of California
assemblages. Because neither large trawls or grab samples were taken in
this environment, there can really be no valid comparison between the
other assemblages and this one. What was taken by this gear should be
mentioned, nevertheless, as these same devices were used in conjunction
with other gear in other parts of the Gulf and did not produce this com-
bination of faunas elsewhere. The living faunas are largely epifaunal,
since most of the dredges were taken on a rock or gravel bottom. Those
living species unique to the northern basins are listed below:

Hexacorals

Octocorals

Balanophyllia, sp.

2 Stat.

Acanthogorgia, sp. nov.

2 Stat

Coenocyathus bowersi

1 Stat.

Callogorgia flabellum

1 Stat

Desmophyllum crista-galli

3 Stat.

Eumuricea horrida

1 Stat

Dendrophyllia cortezi

1 Stat.

Eumuricea, sp. nov.

1 Stat

Brachiopods

Echinoids

Laqueus californianus

1 Stat.

Brissaster totvnsendi

1 Stat

Morrisia horneii

2 Stat.

Hesperocidaris perplexa

1 Stat

Terabratulina kiiensis

1 Stat.

Crustaceans

Gastropods

Salmoneus, sp.

1 Stat

Fusinus traski

1 Stat.

Lamellibranchs

Scaphopods

Macoma siliqua spectri

2 Stat

Cadulus austinclarki

1 Stat.

Nuculana taphria

1 Stat.

Dentalium pretiosum berryi
Siphonodentalium quadrifis-
satum

1 Stat.

Stat.

Asteroids
Astropecien ornatissimus

Stat.

Another 14 species of invertebrates were also taken alive in this environ-
ment, but were also taken at almost the same depths in the central and
southern Gulf. None of the species were abundant as to numbers per
station.

The dead shells collected from the basins and troughs are divided into

80

two groups. The first consists of a large number of local, shallow-water,
sand and rock bottom species, which have either been transported into
deep water through slumps or turbidity currents, or may actually live
there because of high bottom-water temperatures. Probably most of this
group was transported down the steep sides of the basins and channels
through slumping. Some of these species are listed below, while all can be
found in Table II of the appendix.

Gastropods

Lamellibranchs

Acmaea, sp.

2 stat.

Barbatia alternata

1 stat

Fissurella, sp.

1 stat.

Barbatia baileyi

1 stat

Diodora alta

1 stat.

Barbatia gradata

1 stat

Diodora aspera

1 stat.

Anadara cepoides

2 stat

Turbo, sp.

1 stat.

Glycymeris midticostata

1 stat

Crucibulum scutellatum 1 stat.

Pecten vogdesi

1 stat

Crepidula onyx

1 stat.

Cyclopecten pernomus

1 stat

Natica chemnitzi

1 stat.

Pododesmus cepio

1 stat

Polinices otis

2 stat.

Crassinella varians

1 stat

Cypraea annettae

1 stat.

Cardita megastropha

1 stat

Ficus ventricosa

1 stat.

Trigoniocardia guanocastensis

2 stat

Olivella, sp.

1 stat.

Ventricolaria isocardia

2 stat

Pyrene fuscata

1 stat.

Semele, sp.

1 stat

Mitra crenata

1 stat.

Corbula marmorata

1 stat

Hindsiclava andromeda 1 stat.

Pleuroliria oxytropis

1 stat.
Scaphopods

Dentalium oerstedii

2 stat.

Dentalium vallicolens

2 stat.

Cadulus perpusillus

4 stat.

Most of these species were found as shells at depths exceeding 300 meters,
far below their living occurrence, since many of them live only intertidally
to a few meters depth on the rocks which line these deep and very steep-
sided channels.

The other group of dead shells is far more interesting and leads to
considerable speculation as to how they got there. This assemblage of
moUusks was so distinct that they formed one of the most clear-cut
associations in the computor matrix. Of the nine species showing this
strong association, only one was collected alive (once) in the northern
basins, although three more were also taken alive on the upper slope in
the Central Gulf. The nine species showing strong affinities for each
other are listed here.

81

Gastropods

Nuculana taphria

5 Stat

Turritella, sp. (cf. cooperi)
Nassarius miser

6 Stat.
8 Stat.

Cardita barbarensis
Lucina tenuisculpta

13 Stat
10 Stat

Lucinoma annulata

14 Stat

Lamellibranchs

Nemocardium centifilosurn

20 Stat

Nuculana hamata

8 Stat.

Hiatella arctica

6 Stat

Without exception, all have been taken off the CaHfornia coast, most
do not occur south of San Diego on the outer Pacific coast, and all are
continental shelf species, seldom found living in depths of more than
180 meters. The stations which were held in close association by this
peculiar assemblage of dead shells by computer analysis are located on
fig. 26. The list of so-called "California shelf" species, and the number of
station occurrences within the matrix stations is given below. The signi-
ficance of this assemblage is discussed further on pages (123-125).

Gastropods

Calliostoma gemmulatum 1 stat.

Calliostoma variegatum 2 stat.

Margarites albolineatus 1 stat.

Turcica caffea 2 stat.

Turritella, sp. 6 stat.

Pterynotus carpenteri 1 stat.

Boreotrophon, sp. 3 stat.

Nassarius miser 5 stat.

Fusinus barbarensis 1 stat.

Antiplanes abarbarea 1 stat.

Lamellibranchs

Acila castrensis 5 stat.

Nuculana taphria 4 stat.

Nuculana hamata 6 stat.

Yoldia martyr ia 1 stat.

Glycymeris corteziana 2 stat.

Cyclopecten vancouverensis 2 stat.

Cardita barbarensis 8 stat.

Dimya californiana 1 stat.

Lucina tenuisculpta 6 stat.

Lucinoma annulata 6 stat.

Tellina carpenteri 4 stat.

Tellina bodegensis 2 stat.

Macoma planuiscula 3 stat.

Hiatella arctica 5 stat.

A few of the typical living and dead species of mollusks are shown on
Plate VII. Many more are illustrated in Keen (1958) and Oldroyd
(1925-1927).

IX. Upper slope, central and southern Gulf, 121 to 730 meters.
The depths of between 121 and 730 meters south of the islands separating
the Gulf provide a slightly different fauna from the northern basins,
especially in the number of living invertebrate species. Much of this
difference can be attributed to sampling technique, however. Twenty-four
species were found to be common to both the northern and southern Gulf,
and 31 species were collected alive from 14 stations located on fig. 26.

6 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

82

118' 32*

7 K / V T

* COMPUTOR STATIONS'

* N. GULF BASJNS

* UPPER SLOPE

/N /

7

/

60 MAUTICAL MILES ,
1_

Fig. 26. Location of matrix-associated, plus all other stations, taken in the northern Gulf basin
environment, and all stations occupied in the upper slope environment.

83

As in the northern Gulf basins, a considerable number of dead shallow-
water mollusk shells were found on sand bottom. These arrived there
either from slumping or as a result of lowered sea level during the Holocene.
A list of both living and dead invertebrates from this environment can be
found in Table I of the appendix, while the living species only (with
number of station occurrences) from the 15 stations taken on the upper
slope are listed below. Seven kinds of devices were used to establish this
assemblage (Table III), with various small dredges predominating. They
were: one orange peel grab, two rock dredges, three box dredges, five
shell dredges, one 12-meter and two 3-meter otter trawls. It can be seen
from this list that none of the species was taken frequently enough to
appear in the contingency matrix analysis. Relatively few individuals
were taken at any one station.

Sponges

Amygdalum pallidulum

I Stat

Poecillastra tricornis

1 Stat.

Cyclopecten zacae

1 Stat

Corbula ventricosa

1 Stat

Octocorals

Pandora convexa

1 Stat

Anthomuricea, sp.

1 Stat.

Pycnogonids

Brachiopods

Colossendeis bicincta

1 Stat

Terebratula obsoleta

1 Stat.

Argyrotheca loivei

1 Stat.

Crustaceans

Amphineura
Lepidopleurus (?)

2 Stat.

Sicyonia ingentis
Heterocarpus vicarius
Pleuroncodes planipes

1 Stat

2 Stat

3 Stat

Gastropods
Emarginula velascoensis (?)
Solariella permabilis
Calliostoma, sp.
Polinices intemeratus

2 Stat.
1 Stat.
1 Stat.
1 Stat.

Paguristes holmesi
Cancer porteri
Stenocionops beebei
Ethusa ciliatifrons
Squilla, sp.

1 Stat
1 Stat.
1 Stat.
1 Stat.
3 Stat.

Nassarius insculptus gordanus
Nassarius miser

1 Stat.
1 Stat.

Asteroids

Fusinus colpoicus

1 Stat.

Astropecten calif or nicus

Cancellaria, sp.

1 Stat.

Fisher (adult)

1 Stat.

Clathurella thalassoma

2 Stat.

Scaphopods
Dentalium splendidulum
Cadulus californicns

Lameilibranchs
Solemya valvulus
Nucula cardara

1 Stat.
1 Stat.

1 Stat.

2 Stat.

Holothurians
Pseudostichopus mollis 1 stat.

Ophiuroids
Schizoderma diplax Nielsen 1 stat.

Amenichondrius granulosus

Fisher 1 stat.

84

One can also see from this list that the number of species living on the
slope is sharply reduced from the number found on the shelf. One ex-
planation for this, at least in the Gulf of California, is that these depths
are located in the upper portion of the oxygen-minimum zone (fig. 9).
Difficulty in sampling on the very steep slopes characteristic of this
environment may also contribute to the lack of species in this collection.
Some of the more characteristic mollusks are figured on Plates VII and

IX, while others are illustrated in Keen (1958).

X. Middle continental slope, 731 to 1,799 meters.

The middle continental slope, with its steep, dissected topography, is
possibly the most difficult environment in the Gulf to sample adequately.
Of the 12 stations taken in these depths, only four were occupied in the
Gulf of California. Two more samples from slope depths were taken in the
Sal Si Puedes Channel in the northern Gulf but were discussed under the
basins and troughs environment. Since so few samples were taken in the
Gulf proper, and the ecological conditions are so nearly uniform at these
depths along the Pacific coast south of San Diego, all stations taken be-
tween 900 and 1,800 meters along the Middle American coast were in-
cluded in the tabulations. These stations are: 39, 40, 84, 90, 127, 135,
138, 214, 215, 216, 221 and 273. Station locations and data can be found
in the station data list in the appendix. The devices used for these 12
stations were: four 1/5 m- Petersen grabs, three deep diving dredge hauls,
one 12-meter, one 10-meter and one 5-meter otter trawls and two rock
dredges. Bottom water temperature values for the 12 stations ranged
from 3° to 6"C., and thus could be considered lower bathyal in classi-
fication. Much of the middle slope region is also characterized by very low
oxygen concentrations of .5 to .9 ml/L (fig. 9). Only 30 species of inverte-
brates have been identified from these 12 stations, six of them being found
as dead shells only. Only three species of invertebrates were taken twice:
the crustaceans, Acanthephyra curtirostris and Paralomis multispina; and
the pelecypod, Solemya agassizi. The low oxygen concentrations and
inadequate sampling of these depths probably accounts for the small
number of invertebrates in this region. A complete list of the invertebrates
is given below. A few of the mollusks are illustrated on Plate VIII.

Hexacorals Stachyptilum superbum

Cyathocerus, sp. (dead) Swiftia, sp. (afF. S. pacifica)

Octocorals
Distichoptilum, sp. nov. Monoplacophorans

Pennatula phosphorea californica Neopilina galatheae (dead)

85

Gastropods
Solariella nuda
Turcicula bairdii (dead)
Cocculina diomedae (dead)

Lamellibranchs
Solemya agassizi
Lucinoma, sp. nov.
Vesicomya lepta (dead)

Cephalopods
Argonauta pacifica (dead)

Solenogasters
Prochaetoderma, sp. nov.

Crustaceans
Benthesicymus tanneri
Heterocarpus affinus

Heterocarpus, sp. nov.
Paracrangon areolata
Glyphocrangon spinulosa
Acanthephyra curtirostris
Axiopsis {Calocarides), sp. nov.
Munidopsis, sp.
Parapagurus pilasimanus
Neolithodes diomedae
Paralomis multispina
Paralithodes rathbuni
Gnathaphausia zoea

Holothurians
Molpadia musculus (violaceum type)
Molpadia musculus {musculus type)
Synallactes ishikawa

XI. Abyssal southern borderland basins, and outer
continental slope, 1,800 to 4,122 meters.

The abyssal region represents a complete change from the previously
discussed deep-water environments, both in the diversity of fauna and the
great abundance of individuals. Although only 15 stations were occupied
at these depths, 186 species of benthic invertebrates have been identified,
and many more are yet to be checked by specialists. Whereas in most of
the shallower slope stations a species would be represented by only a few
individuals, the species from the abyssal regions were extremely abundant,
often comprising hundreds of individuals per station. The richness of
fauna actually approaches that of the inner continental shelf.

Bottom-water temperatures within this environment range from 1.2°
to 2.6°C. (fig. 11), which can be considered characteristic of true abyssal
conditions. The oxygen values ranged from 1 to 2.8 ml/L., being high
enough to support most forms of marine life. All stations except one were
taken on pure silty clay bottom. The one exception was taken on clay
with appreciable amounts of manganese crust. This environment differs
from that of the middle continental slope in having lower bottom-water
temperatures, much higher oxygen, and occurs on a relatively level, silty
clay bottom, whereas the middle slope is characterized more by steep
rocky and sandy bottom. Only five of the 86 species from the abyssal
basin and slope environment were also found at middle slope stations.
One species, the pelecypod, Chlamys latiaurata monotimeris, lives on kelp
fronds, thus falls to the bottom wherever kelp drifts; one is a hermit crab,

86

Parapaguriis pilosimamis, with a wide distribution; one a holothurian,
Molpadia musciiliis, also with an extremely wide distribution in all seas;
another is a bathypelagic shrimp, Acanthophyra curtirostris ; and the fifth
is the pelecypod, Solemya agassizi, which was rarely taken alive, and
being very light (mostly periostacum) may possibly float some distance.
Although these stations, shown on fig. 3, were taken in abyssal depths,
most of them were less than 100 nautical miles from land, as the shelf is
very narrow along the Pacific coast of Mexico and deep basins lie very close
to land. This proximity to land may well explain the richness of fauna,
since upwelling and associated high surface productivity seem to be typical
of most of the areas where trawling was carried out. This high surface
primary production provides a rich accumulation of organic matter on the
bottom, both in the borderland basins, and on the slopes which descend
directly to the abyssal sea floor (Parker, 1961). The majority of the
invertebrates appear to be detritus or deposit feeders, which should thrive
in the organic-rich bottoms. A complete list of the invertebrates identified
so far from the 15 stations is given below. Of the 20 stations (successful
and unsuccessful) taken at abyssal depths all but two (1/5 m- Petersen
grabs) were made with various large trawling devices (Table III), similar
to those used by the Galathea and Albatross. For this reason, few small
animals were collected. These devices were: one mid-water trawl (on
bottom), six deep diving dredges, three 3-meter Agassiz beam trawls,
and of the one 12-meter, six 10-meter and one 5-meter otter trawls.
The mesh size of the bags for all of the trawling devices, including deep
diving dredge, was the same, as all net liners were made by the same men
from the same bail of material, being about 1 cm. in diameter. Many of
the typical mollusks are illustrated on Plate IX, X or can be seen in
Dall(1908).

Octocorals
Anthomastus fitter i
Thouarella, sp.
Sckroptilum cf. durissimum

Hexacorals
Caryophyllia diomedaea

Polychaetes
Maldane, sp.

Brachiopods
Macandrevia americana diegensis 2

Pogonophora
Galathealinum bruuni (?)

Monoplacophorans
Neopilina galathaea

Gastropods
Puncturella cf. expansa
Solariella ceratophora (dead)
Solariella equatorialis 2
chitonous trochids (?)
Fusinus rufocaudatus
Tractolira sparta

87

Gastropods (continued)
Gemmula, n. sp. (aff. G. exulans) (dead)
Pleurotomella clarinda
Steiraxis aulaca

Nudibranchs
Bathydoris aioca

Scaphopods
Dentalium megathyris 5

Lamellibranchs
Solemya agassizi
Nucula panamina
Nuculana agapea
Malletia truncata
Tindaria compressa
Area corpulenta pompholynx
Area nueleator 2
Limopsis compressus 6
Chlamys latiaurata monotimeris 2 (dead)
Cyclopecten, n. sp.
Vesicomya, sp. (dead)
Abra profundorum
Cuspidaria panamensis 2
Myonera garretti 2
Poromya perla

Crustaceans
Storthyngura aff. pulchra
Paropsurus giganteus
Benthesicymus altus 2
Hymenopenaeus doris 2
Sergesies phorcus
Pandalopsis ampla
Pontophilus occidentalis
Glyphoerangon, n.sp. (aff. longirostris)
Lebbeus, sp. 2
Nematocarcinus cf. ensifer
Acanthephyra brevirostris
Acanthephyra curtirostris 2
Aeanthephyra, n. sp. (aff. sibogae)
Munidopsis, sp.
Munidopsis bairdii 2
Parapagurus pilosimanus 3
Paralomis verrilli
Ethusina faxonii

Pycnogonids
Colossendeis angusta 2
Colossendeis bicincta
Colossendeis colossea
Colossendeis macerrima
Pallenopsis californica 2
Ascorhynchus agassizi

Holothurians
Bathyplotes, sp.
Pseudostichopus mollis
Oneirophonta mutabilis
Peniagone, sp.
Benthodytes sanguinolenta 4
Psychropotes dubiosa
Psychropotes raripes
Abyssocueumis abyssorum 3
Sphaerothuria bitentaeulata
Molpadia granulosa
Molpadia musculus forma musculus
Molpadia musculus forma spinosum
Molpadia musculus forma violaceum

Echinoids
Aporocidaris milleri 3
Kamptosoma asterias
Tromikosoma panamense 2
Tromikosoma hispidum
Urechinus loveni 2
Brisaster latifrons

Asteroids
Eremicaster pacificus (Ludwig)

Ophioroids
Ophiura irrorata Lyman
Ophiomusium glabrum Liitken and

Mortensen
Amphiura seminuda Liitken and

Mortensen
Amphiodia digitata Nielsen
Amphilepis patens Lyman
Amphioplus hexacanthus H. L. Clark
Ophiomusium lymani Wyville Thomson
Ophiacantha setosa Lyman

Numbers indicate number of station occurrences. Species without numbers were taken only
once. Those taken dead only are indicated.

XII. California borderland basins, 1,641 to 2,358 meters.

The California outer borderland basins are found in depths normally
considered abyssal, but seem to have a fauna quite different from that of
equivalent depths to the south. Although this area (fig. 3) is not within
the strict area under consideration in this paper, it is important to indicate
these differences, and to list the fauna found there. The author was
fortunate to be consulted concerning fauna present in three areas along
the California coast from Los Angeles to San Francisco, as part of a study
of atomic waste disposal grounds, carried out by the Advanced Systems
Division of the Pneumodynamics Corporation. Nine 5-meter otter trawl
stations (Table III) were taken in depths of from 1641 to 2358 meters,
four in the Santa Cruz Basin off Los Angeles, three in the Farallon Basin
off San Francisco, and two in a small unnamed basin off Point Arguello.
Although the trav/ls used in the California borderland basins were smaller
than many of those used in the abyssal regions off Mexico, the inner liners
of the nets were of same mesh size. Catches were of comparable size, and
the individual animals were also of the same size in both regions. The
basic composition of catches from the two regions were also similar, i.e.,
equal amounts of ophiuroids, asteroids, mollusks, polychaetes, etc. Tem-
peratures ranged from about 2.5° to 4°C., and oxygen about 1 to 1.5 ml/L.,
while the sediments were all silty clay.

None of the basins was completely closed, such as those described by
Hartman and Barnard (1958), and seemed to be well-oxygenated and
flushed by bottom currents. In configuration and environmental character-
istics these three areas differed little from the basins studied in the deep
borderland off Baja California, therefore it was somewhat surprising to
find such a completely different fauna there. All three areas were very
rich, both in species and in individuals. For instance, one short trawl
with a small 15 foot "try" net, produced two large tubs of living animals,
including hundreds of specimens of a small pecten, Cyclopecten randolphi
tillamookensis. One surprising aspect of this basin fauna was its close
affinity with bathyal and shelf fauna of the northern Pacific. Many of the
species were formerly known only from the Gulf of Alaska, and in the
vicinity of the Bering Sea and the Kamtchatka Peninsula. None of the
animals was typical of those collected by the Albatross in Central
American waters. This would suggest that there is some zoogeographic
separation in the deep sea, which parallels geographic breaks along the
shore. It also suggest that there is a migration south of many species

89

along the coast from Alaska terminating at San Diego. The flow of the
California Current over this same region may influence this faunal distri-
bution, although it is difficult to see how certain species of Buccinid
gastropods could be distributed south by currents, as they have direct
development from egg capsules, even though shallow-water Buccinid
capsules often drift ashore.

Only three species of invertebrates, the shrimp, Pandalopsis ampla,
the Galatheid shrimp, Munidopsis bairdii, and the kelp scallop, mentioned
previously, occurred in both the northern and southern borderland. None
of these species lives on or attached to bottom, so could be expected to
occur anywhere. A large number of holothurians, asteroids, ophiuroids,
sponges, polychaetes, sipunculids, anemones and pycnogonids were taken
at these stations, but many were ashed before identification in order to
test for radioactivity. The rest have not yet been identified by specialists.
The remaining specimens have been deposited in the Invertebrate Col-
lection at Scripps Institution. A complete list of the identified animals is
given below. A few of the mollusks are illustrated on Plate VIII, but
unfortunately the majority were ashed for remanent radioactivity studies.

Gastropods
Margarites cf. beringensis
Gaza rathbuni
Solariella, sp. (dead)
Buccinum diplodetum
Ancistrolepis magnus
Chrysodomus liratus
Colus halidomus
Colas hypolispis
Colus trophius 3
Cryptogemma adrastia
Cryptogemma calypso
Antiplanes vinosa (dead)
Leucosyrinx erosina
Leucosyrinx persimilis

Scaphopods
Dentalium cf. agassizi
Dentalium cf. rectius
Cadulus cf. tolmiei

Malletia faba 2

Chlamys I. monotimeris (dead) 2
Cyclopecten r. tillamookensis 2
Vesicomya stearnsi 2
Cuspidaria cf. beringensis
Dermatomva leonina

Crustaceans
Pandalopsis ampla 3
Crago abyssorum 3
Callianassa goniopthalma
Munidopsis cf. bairdii
Munidopsis verrilli
Acanthalithodes hispidus
Chionoecetes tanneri 5

Sipunculids
Phascalosoma, sp. (?)

Lamellibranchs
Solemya cf. johnsoni 2
Nucula savatieri

Crinoids
Afelecrinus, sp. (?)

90

Holothurians Ophiuroids

Laetmophasma fecundum (?) Ophiura liilkeni (Lyman)

Pannychia moseleyi (?) Amphiodia urtica (Lyman)

Ophiacantha normani (Lyman) 2

Numbers indicate number of station occurrences. Species without numbers were taken
only once.

Discussion

In order to provide explanations for the presence of distinct faunas in
these 12 environments just described and shown areally in fig. 27, one
must not only examine the physical characteristics of the environments,
but also the geological history of the region and the biology of the species.
The environmental boundaries are suggested both by the physical factors
and the distribution and abundance of the more important index animals.
One can readily see that a correlation is indicated between the distribution
of certain physical factors, such as temperature, depth, sediment type,
turbulence, oxygen and salinity, and the geographical limitations of most
invertebrates, since the distributional patterns of both the species and
physical factors coincide. On the other hand, the presence of some species
or even whole assemblages may not be determined by the physical factors
alone, but indirectly by biological factors, such as food preferences (which
in turn are mainly determined by feeding mechanisms), competition for
food, predator-prey relationships, reproductive capacity and larval
development, commensal or parasitic relationships, etc.

One could gain an even better understanding of the organization of these
aggregations of animals if it were possible to determine numbers and
weights (biomass or standing crop) of the dominant and major sub-
dominant organisms within the assemblage. For instance, if the percentages
or biomass of animals involved in these various biological activities
(feeding and reproduction) were known within each community, some idea
of the energy relationships involved to sustain these communities could
be ascertained. This achievement has rarely been achieved for one assem-
blage, except by Sanders (1960), and no comparisons of this sort exist
for a number of assemblages in a single region, or between assemblages
from many regions. Unfortunately, standing crop and biomass figures
are not available for this study.

Before discussing these various biological activities for each assem-
blage, it is first necessary to define the various terms used here. Feeding
types of invertebrates have been defined time and time again, so that

91

there is some confusion existing between what is considered, for instance,
a filter (and or) suspension feeder. Rather than give all of the previous
definitions, most of which can be found in Yonge (1928) and Jorgensen
(1955), only the ones which apply to this study are presented. The feeding
types dealt with in the following discussion are 1) suspension feeders.
These animals are those which both propel and filter their food from the
surrounding waters, i.e. they may take food, both living and dead, from
the water by bringing this water into contact with their feeding mech-
anisms, and often filtering out this food, passing the remaining water out
of their systems. Their filters may be adjusted for various size food particles,
or else, the water currents may be such that only large particles or larger
animals are brought into contact with grasping mechanisms. Some of
these suspension feeders may actually feed on deposits, or at least on
soupy detrital material occurring just off the bottom, until unwanted
particles tend to clog the filtering apparatus to such a degree that more
energy is expended in getting rid of the unwanted material than in gaining
food. For this reason, suspension feeders are at their best advantage in
clear waters on a hard bottom. Type 2) discussed here is the deposit
feeder. Deposit feeders gain their food directly from the bottom sediments
or in the soupy organic layer on the surface of the sediments. In the rather
limited number of species of lamellibranchs, they may use palps, which
are highly developed sorting organs, or have long, prehensile inhalent
siphons for picking up living and dead material from the sediments. Other
invertebrates may be non-selective deposit feeders, such as holothurians
and most polychaetes ingesting the whole sediment, extracting the food
while the sediment is passing through the animal, and expelling the unused
inorganic material. 3) Predators or carnivores are those animals which
prey on or capture living food, particularly the more motile organisms.
Many large gastropods, certain asteroids, many crustaceans, and even one
group of lamellibranchs (Cuspidaria) fall into this group. 4) Algae feeders
and/or browsers are, in this paper, those animals which are primarily
herbivores, feeding either on diatom films, bryozoans, sponges, etc. on a rock
or sandy surface, or feeding directly on attached vegetation. 5) The
scavengers or carrion feeders feed primarily on dead flesh, although
may also be predaceous when carrion is not available. .Some animals which
fall into this category are certain Buccinid snails and many crustaceans.
Finally, there are the parasites, feeding directly on a host and eventually
killing it, and commensal organisms, which may feed on or depend upon
a host to get their food, without harming it. Other feeding types certainly
do exist, but are modifications of the above types and are not discussed here.

92

Certain larval types are also mentioned in the following discussion, most
of which are associated with molluscan development. It is within the
mollusks that one of the greatest varieties of larval development is found;
as most of the other invertebrate groups have a pelagic larval development,
swimming about in the surface or surrounding waters for a considerable
length of time (most echinoderms), or several successive larval stages,
which may be free-swimming or passing part of their existence as parasites
(most crustaceans, although not malacostracans). Lamellibranch species
may have planktotrophic or pelagic larval development, where the veliger
or trochophore larvae may spend anywhere from a few hours to several
weeks swimming about in the water before settling. Others may have a
lecithitrophic development, where the larva is furnished with considerable
food in its egg and may either have a direct development from the egg
without a pelagic existence, or else the pelagic existence is very short
and the larvae does not feed before settling. Other lamellibranchs may
even have brood protection, sheltering their young until they are ready
to take up a direct development, without a trochophore stage. Gastropods
have an even more varied larval development, ranging from those species
which have trochophore larvae with pelagic stages lasting more than a
month to those that lay relatively few large eggs from which young snails
hatch and crawl away, or those that even bear living young in the image
of the adult. An extensive discussion on reproduction and larval develop-
ment of invertebrates can be found in Thorson (1950).

An examination of existing literature on present-day marine benthic
communities, as well as many fossil assemblages, led to the conclusion
that a basic organization of animals living together results from an inter-
dependence of biological factors and an overall dependence upon the
physical environment (see Hesse, Allee and Schmidt, 1951 and Thorson,
1950). The environmental extremes not only influences the physiological
processes of the dominant or characteristic animals, but it may exert a
control on the distribution and abundance of food, especially plankton
and organic detritus. Thorson (1957) has proposed that parallel bottom
communities, characterized by the same or closely related genera of
dominants, exist wherever environmental conditions are similar. Perhaps
these parallel communities are not so parallel in generic compositions as
they are in the biological organization of the community as suggested in
part by Hesse, Allee and Schmidt (1951). One type of community found
in all waters with the same set of environmental conditions may be char-
acterized by particular percentages of feeding types and dominated by
animals with certain kinds of reproduction or larval development. It is

93

not necessary that the genera, or even families, are the same for the
dominant organisms in these parallel communities, so long as the dom-
inants perform the same function within the community. These "ecological
parallel communities" have been designated "ISO-communities" by
Thorson (1957, p. 504); although this concept has recieved earlier dis-
cussion by TiscHLER (1950, 1951) and Gaspers (1950). For this reason,
a preliminary analysis of the feeding types (when known) of the char-
acteristic animals of each environment was made, and a few conjectures
as to the organization of the assemblages as to other biological factors
are presented in the discussion of the results of this study. These assem-
blages have also been compared with similar assemblages or communities
studied elsewhere in the tropics and sub-tropics, and in particular those
described previously by the author from the Gulf of Mexico. Finally,
an attempt is made to determine which of the environmental factors
exerts the greatest influence upon the assemblage as a whole. The discussion
of these assemblages follows in the same order as the earlier descriptoins.

I. The Intertidal and Shallow Rocky Shores:

In all probability, the rocky shore habitat in the Gulf of California
may offer one of the richest examples of this sort in the variety of species
and numbers of individuals known in the world. The rocky shores of the
temperate or boreal regions may be richer in numbers of individuals but
there are far fewer species. The rocky shores of most tropical islands also
seem to be relatively poor in numbers of species and individuals, at least
from personal observations made on islands in the Indian Ocean, on
Easter Island and in the Bahamas. Longhurst (1958, pp. 54-59) cites
relatively few intertidal rocky shore invertebrates in his discussion of the
shallow, hard substrate community along the coast of Sierra Leone, West
Africa. This would indicate that it is not the tropical climate alone which
is responsible for the large number of species found on the rocky shores of
the Gulf of California.

Although this assemblage of animals is found everywhere in the world
where rocky shores exist, there was no exact counterpart in the Gulf of
Mexico, with which this author is most familiar. The closest approximation
to this assemblage off Texas is the fauna of the rock jetties at the major
passes along the northern Gulf coast, described by Whitten, Rosene
and Hedgpeth (1950). There is little resemblance between their list and
the one given here, except for a few moUusks. This is not surprising, since
there are no natural rocky shores for the recruitment of the species adapted
to this habitat along the coast of the northern Gulf of Mexico, while it is

94

the prevalent habitat for the major portion of the shoreline of the Gulf
of California.

The rocky shore assemblage is entirely an epifaunal one, dominated by
algae (or diatom film) and suspension feeders, plus a number of inverte-
brates which prey upon the others. Since a rock bottom is not conducive
to the accumulation of detritus (except under the rocks), deposit feeders
are virtually absent. Savilov (1961), in a similar study of feeding types
in the Okhotsk Sea, states that sessile suspension feeders dominate the
rocky shores. The majority of the gastropods are adapted to living in a
rigorous environment, and nearly all of the lamellibranchs possess byssal
threads by which they attach themselves firmly to the rocks. Some of the
forms are thought to have a rather long planktonic development, per-
mitting a wide dispersal over long stretches of coast line while many of
the prosobranchs develope from egg capsules, which guarantee that they
will be retained on the rocks and not swept into an unfavorable environ-
ment (Thorson, oral communication). According to Thorson (personal
communication), many of the larvae of intertidal invertebrates also exhibit
strong negative and positive phototropisms, which would facilitate settle-
ment at the proper time during the tidal cycle, so as not to be swept off
their selected place of attachement during early stages of settling. There is
little doubt that the feeding habits and types of reproduction of the
major components of this epifaunal community are similar on all rocky
shores throughout the world. Many of the same characteristic genera
{Littorina, Ostrea, Mytilus, Fissurella, Balanus and Bugula) occur nearly
everywhere, although tropical shores are often characterized by many
more genera and species and fewer individuals of each than temperate or
boreal regions. The environmental factors exerting the most influence upon
this assemblage are certainly rocky substratum, great turbulence, extreme
range of water temperature, high oxygen and normal oceanic salinities.

Most of the fossil assemblages studied in the Baja California region and
in the Gulf of California are of Pliocene to Pleistocene age. All of them are
composed of a mixture of intertidal rocky shore and nearshore shelf
assemblages. Discussions of these deposits can be found in Hertlein and
Emerson (1959), Emerson (1956 and 1960a), and Addicott and Emerson
(1959). Only two recent papers describe fossil assemblages from the Gulf
of California proper, one by Emerson (1960a) on the Pleistocene inverte-
brates of Ceralvo Island, and the other by Hertlein and Emerson (1959)
on the Pleistocene fauna of the Tres Marias Islands. An earlier review of
the paleontology of the Gulf of California can be found in Durham (1950).
Of the 34 species of invertebrate fossils from Ceralvo Island listed by

95

117* 3Z 116'

31" 114 113'

\3

4

N

N

\;

\

y

106' 2tf 105'

Fig. 27. Areal distribution of the Gulf of California environments. Distribution of the intertidal
environments is shown on figure 14. Stippled area near the head of the Gulf was not sampled
adequately enough to .designate environments and thus does not represent any specific

environment.

96

Emerson, only 12 can be considered part of the rocky shore assemblage.
Two corals were also cited which are now living at Maria Cleophas Island
and Cape San Lucas. The rest of the fossil moUusks from Ceralvo Island
belong to the shallow, nearshore shelf environment, and as Emerson states,
it is a mixed fauna resulting from the reworking of the attached and non-
attached elements of that region. The Pleistocene fauna from Maria
Cleophas Island (Hertlein and Emerson, 1959) is primarily a level-bottom
fauna. Of the 28 species found at this locality, only eight were attaching
forms usually found on intertidally exposed rocks. This seems somewhat
surprising, since most of the present shoreline of Maria Cleophas is rocky,
and the surrounding shelf is very narrow, providing little level bottom for
the majority of these species which prefer this habitat. This very narrow
shelf was observed personally in a survey around the island in 1959
(FoosE, 1962). Few of the rocky shore animals cited in the present survey
are listed from the fossil deposits in northwestern Baja California, although
the majority of the fossils are rock-living species normally found on the
California coast (Emerson, 1956; Addicott and Emerson, 1959; and
Emerson and Addicott, 1958). A discussion of the fossil corals from the
Gulf of California, some of which were taken intertidally in the present
study, can be found in Squires (1959).

II. Intertidal Sand Beach and Sand-Flats to 10 Meters:

This assemblage is quite similar in composition throughout all warm-
temperate to tropical regions of the world where sand-flats and beaches
exist (Pearse, Humm and Wharton, 1942, Schuster, 1956, and Gauld
and Buchanan, 1956). For instance, a comparison of the surf-zone and
inner shelf, sand bottom assemblages of the northern Gulf of Mexico
(Parker, 1960, pp. 320-321) with its equivalent in the Gulf of California
reveals a great many similarities, especially at the subgeneric level of
mollusks and crustaceans. For nearly every species of moUusk, crustacean
and echinoderm listed for the Gulf of Mexico nearshore sand-bottoms,
there is an equivalent species in the same environment in the Gulf of
California. Many of the species from both Gulfs can be considered twin
species, with common ancestors in the Miocene and Pliocene of Panama
and Columbia (Olsson, 1961), which at that time was an open seaway
between the Caribbean Sea and the Pacific Ocean. This phenomenon has
been discussed at length for several invertebrate groups and fish by
Ekman (1953, pp. 30-38). The principal difference between the two regions
is that there were many more species in this environment in the Gulf of
California, even though sand beaches are the dominant feature of the coast

97

of the Gulf of Mexico and constitute less than half of the shoreline of the
Gulf of California. The great variation in the size and sorting of sand
particles along the coast of the Gulf of California, as compared to only
very fine, well-sorted sands which are found along the northern Gulf of
Mexico coast, may account for the greater diversity of animals in this
environment in the Gulf of California. A greater range of water temper-
ature (0° to + 40° C.) in the northern Gulf of Mexico, as opposed to only
15° to 30° C. in the Gulf of California may offer an even better explanation
for lower species diversity in the Gulf of Mexico.

Buchanan (1958) and Bassindale (1961) investigated the inshore
sand-bottom community in the tropics off Accra, Ghana, which is in the
same temperature province as the Gulf of California. Buchanan reports
two species of Donax, one of Tivela, a Bulla, a Terebra and an Olivella
from the surf zone, the same genera which are common to the surf zone
from somewhat deeper water in 6 to 15 meters on fine sand, which also
contains the same components as the inshore sand bottom community in
the Gulf of California. A complete list of these sand beach and sand flat
species of invertebrates off Ghana can be found in Buchanan (1958,
pp. 19-21) and Bassindale (1961, pp. 500-507). Longhurst (1958) in
his study of bottom communities off Sierra Leone, just north of Bucha-
nan's region, designated the shallow, nearshore sand-flat assemblage as
the Tellina iso-community. The dominant animals of Longhurst's Tellina
iso-community are Donax (= Tellina), Terebra, and a suspension feeding
polychaete, Spio, sp. The less abundant members are a polychaete (Siga-
lion), an amphipod (Urothoe), a Hippid crab {Albunea) and another species
of the gastropod, Terebra.

One region of nearshore sea bottom in the tropics which seems to be
quite different from those discussed previously is located on the Malabar
coast of India. Seshappa (1953) collected a number of grab samples in
this region in depths to about 10 meters. The bottom temperature range
was from 26° to 30° C. (similar to that off Mazatlan), but because of the
Monsoons, salinities fluctuated widely from season to season (16°/oo to
35''/po). Seshappa's nearshore sand community bore little resemblance to
either its counterpart in the Gulf of California or those studied off West
Africa. A polychaete, Prionospio, was the only dominant, and Lucina
was the only genus of nine molluscan genera found there that was also
represented in an equivalent environment in the Gulf of California.

It is impossible to obtain a quantitative conception of this assemblage
in the Gulf of California, since so many of the shallower samples from the
surf zone were taken by hand collecting. It was observed, however, that

7 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

98

within the surf zone, Heterodonax was exceedingly abundant in certain
localities and large handfuls could be taken easily at the water's edge.
Various species of Donax were abundant as dead shell, but very few living
specimens were observed at any time. Great numbers of Tiirritella shells
were observed in freshly-deposited strand lines along the shore, but none
were collected alive, not even by means of grab samples taken fairly close
to shore. Emerson and Stillman Berry (personal communication)
reported abundant living populations of Turritella just outside the surf
zone in the Puerto Penasco and Guaymas regions. Buchanan (1958) found
Turritella in large numbers at the shelf edge, while Turritella is found at
intermediate shelf depths in European boreal waters (Thorson, 1957).
The most abundant living gastropods were the Olivellas, Olivas and
Terebras.

Eight bottom grab samples were taken in depths of 5 to 11 meters on
sand bottom, using a small 1/20 square meter Van Veen grab. The living
mollusks found in these stations (shown below) give an idea of the relative
abundance and diversity of animals which can be found in small samples
from this environment.

Station Number

of Inc

lllUtl

lividuals

Species

4

1

Nuculana elenensis

(P)

1

Lucina cancellaris

(P)

1

1

Ctena clarionensis
Transenella puella

(P)
(P)

Total

4

5

3

Nucula declivis

(P)

9

Tellina felix

(P)

2

Tagelus politus

(P)

Total 14

6 (296)

2

Laevicardium elenense

(P)

1

Megapitaria squalida

(juv.)(P

Total

3

7

1

1

Kellia suborbicularis
Tellina felix

(P)
(P)

Total

2

11

1

Terebra variegata

(G)

2

Laevicardium elenense

(P)

2

Tivela delesserti

(P)

1

Tellina amianta

(P)

Total 6

99

o • XT u Number _

Station Number ^ ■, :,■ -, , Species

or Inaividuals

111 None living

1 13 Total 1 Olivella anazora (G)

114 1 Olivella fletcherae (G)
1 Megapitaria aurantiaca (P)
1 Transenella puella (P)
3 Macoma, sp. (juv.) (P)

Total 6
P = Pelecypod G = Gastropod.

Only 36 living specimens of mollusks were taken in these eight small-
sized samples: no other groups have been identified yet from these stations.
If these samples cover 1/20 m^ each or a total of 2/5 m^ the average number
of animals per square meter is roughly 90. This figure is not too reliable,
since not only is the total area sampled insufficiant, but the distribution
of animals is very patchy in this environment. This can be seen by the
variation in the number of individuals in the eight stations. The majority
of the living individuals of mollusks from these stations were very small,
and almost juvenile in size.

A preliminary appraisal was made of the feeding types among the
invertebrates of the near shore, sand-bottom assemblage. The dominant
feeding type among the lamellibranchs appears to be suspension feeding,
which was also observed by Sanders (1958), Savilov (1961) and McNulty,
Work and Moore (1962). This would seem logical, since the nearshore
zone is characterized by continual turbulence and longshore current
transport, bringing in an abundant supply of suspended organic matter
and living organisms held in suspension. The abundance of light in this
zone also produces a large supply of phytoplankton, one of the principal
sources of food for suspension feeders. Predators comprise the greatest
proportion of gastropods, and as such they are probably dependent upon
the large lamellibranch population.

The relatively few deposit-feeding mollusks can be attributed to the
probable lack of organic detritus, which is not apt to collect in the con-
tinuously agitated and well-sorted sand, so typical of this environment.
Most of the lamellibranch larval shells examined indicated that the majority
of species have a pelagic development while many of the very large proso-
branch gastropods have large, egg-capsuled produced larvae which can
probably withstand the turbulence so typical of these waters. The fact
that so many of the inhabitants of the sand-flat environment are very
active animals and have a long pelagic development may explain the great

100

uniformity of this assemblage over long stretches of coast line, even where
there are considerable portions of rocky coast separating the beaches.

This environment provides the most useful tools for the interpretation
of the Recent geological history of any continental shelf. Many sturdy
mollusk species are confined to this depth, and are thus excellent indicators
of sea level. Presence of members of this assemblage as dead shell on deeper
parts of any continental shelf is usually an indication of previously lowered
sea level unless transported by ice. The presence of submerged shorelines
resulting from the last glaciation was substantiated and dated in the Gulf
of Mexico by using typical mollusk shells of intertidal and nearshore shelf
species (Curray, 1960 and Parker, 1960). Time and again, many of the
Gulf of California species typical of this environment appeared as dead
shell on portions of the middle and outer continental shelf off San Bias
and Hermosillo. They were almost always associated with sand deposits
at preferred depths or on slight topographic highs, which could have
resulted from a once lowered sea level (van Andel, etai, in press). Since
many of the mollusk species in this habitat are subjected to the pounding
of the surf, most of them are quite sturdy and resistant to abrasion. They
are, therefore, the most likely species to remain in place and undamaged
over long periods of geological time. This observation is substantiated by
their abundance in Tertiary fossil localities. Lists of mollusks from un-
consolidated sand and sandstone deposits from the Gulf of California,
compiled by Emerson (1960a) and Hertlein and Emerson (1959), and
presumed to be of Pleistocene age, are dominated by the sand-flat species,
most of which were in a good state of preservation.

111. Low Salinity Lagoons and Mangrove Swamps:

This assemblage, with its abundant populations of oysters, Rangia,
Mytilids, Corbiculids and Penaeid shrimp, closely resembles the low-
salinity, river-influenced assemblage of the northern Gulf of Mexico coasts
(Parker, 1959). The presence of the immense Arcid, Anadara tuberculosa,
the large Corbulas, and many more species of corbiculids in the Gulf of
California lagoons, constitutes the principal difference between the Gulf
of Mexico and Gulf of California faunas. Otherwise, 11 of the 19 listed
species for the Gulf of California lagoons have their exact counterparts in
the Gulf of Mexico. Many of the same genera and sub-genera of mollusks
frequenting these low-salinity areas are also known from similar regions
in South America, Africa and tropical, sub-humid Asia.

It is difficult to determine the dominant feeding type or usual form of
larval development for the low-salinity lagoon assemblage, as so little is

101

known concerning the biology and life history of the common inhabitants
of this environment. It was impossible to determine from the literature,
the type of feeding or development from the Corbiculids, Mytilopsis or
Rangia, although it is suspected that all may be suspension feeders,
specialized to select lighter organic material from the more dense inorganic
particles by some sort of ciliary mechanisms. Of the 18 genera listed for
this environment in the Gulf of California, 55 "/o are probably suspension
feeders. However, about half of these are adapted to high turbidity waters,
such as oysters and Rangia, which can function in high concentrations of
inorganic material, and are in reality feeding upon the deposits. Of the
remaining, 227o are herbivores, 14% are predators or scavengers, and
Melampus can be considered a terrestial herbivore. No estimate can be
made of the usual mode of larval development, except that virtually all of
the large lamellibranchs have planktonic larvae, which are thought to
settle rather rapidly in response to tidal and discharge changes in the
estuaries. Less is known for the gastropods, although Melampus is known
to take up an aquatic existance only to reproduce, the juveniles soon
creeping out of the water to live under damp vegetation along the shore.

The environmental factors limiting this assemblage have been discussed
at length by Parker (1956, 1959 and 1960) for its counterpart in the Gulf
of Mexico. Salinity certainly has a limiting effect in this environment,
since many species die or fail to reproduce whenever salinities rise above
10 or 15%. The extreme range of water and air temperatures encountered
in these shallow waters may serve to exclude many other invertebrate
species which might compete with the lagoonal species which are adapted
to changes of up to 30"^ C. between minimum and maximum. Sediment is
limiting, only when it is too soft to support the populations of oysters and
possibly Anadara. It is known that pH or hydrogen-ion concentrations are
lower in the lagoons and estuaries than in the open sea, but it is not known
whether these low pHs have any effect on estuarine faunas.

This assemblage is relatively uncommon in the fossil deposits surrounding
the Gulf of California, but it comprises a large percentage of shell middens
of the prehistoric peoples in the southern part of the Gulf. The species
typical of low-salinity lagoons are valuable in paleoecological inter-
pretations, since they are excellent indicators of climatic change (dry to
wet or vice-versa) and as in the previous assemblage, good shoreline
indicators. Since they thrive only in waters of low to medium salinity, it
is unlikely that they will be found living in open sounds, gulfs or oceans.
In order for low salinity conditions to be maintained in areas where these
mollusks live, there should be little connection with the open sea. There-

102

fore, lagoonal areas must be part of the shoreline or allied with the terres-
trial environment. The occurrence of estuarine shells at the shelf edge off
San Bias (van An del, et ai, in press) constitutes excellent proof that
a shoreline existed there at one time.

Although not investigated at all in the Gulf of California, the inlet
environment should not be completely neglected, since the very existence
of lagoons and estuaries along the Gulf of California coast means that
inlets or access to these lagoons from the Gulf must also exist. The inlets
were a very distinct and characteristic habitat for the Gulf of Mexico
lagoons and sounds as pointed out in Parker (1955, 1956 and 1959). The
physical factors which set this environment apart from other lagoon or
open ocean areas are: first of all, two-layered, strong tidal currents which
generally sweep the bottom clean creating either a shell-gravel or hard
sand bottom, variable salinities and temperatures, generally in the upper
range of the climate in which they are located, and finally a continual sup-
ply of nutrients, both from the estuarine side and open Gulf or ocean side.

A few observations were made in the inlet into Mazatlan harbor in
April, 1959. One species of mollusk, Atrina (probably mama), certainly
must have been abundant, as native divers were harvesting them in large
numbers and have been doing so for years. This has proved to be one of
the index mollusks for the inlet environment on the Gulf of Mexico coast
also (Parker, 1956 and 1959). Bottom samples were difficult to obtain
as the bottom was too hard, but a few small Van Veen samples did produce
a number of living Olivella, Tellina, Crepidula and small Venerids. All of
these genera were found to be very characteristic in the Gulf of Mexican
inlets as well and seem to be a typical ISO-Tellina community. The
stations from this inlet are: 11, 112, 113, 114, all taken with a 1/20 m"^
Van Veen grab.

No other comparable studies of inlets as distinct habitats for macro-
invertebrates are known to the author, although Henning Lemche
(personal communication) has recognized that the conditions which
characterize inlet environments usually produce a rich nudibranch popu-
lation, as well as a rich growth of algae, bryozoans, hydroids and turbel-
larians. Investigations of similar environments in other parts of the world
produced many of the same characteristic organisms, with the exception
of those mollusk genera which are exclusively tropical, such as Pinna
and Atrina.

IV. Nearshore Sand to Sand-Mud, 11 to 26 Meters.

This environment corresponds closely to the shallow or nearshore shelf
environment off the Mississippi Delta (Parker, 1960), and portions of both

103

the nearshore and intermediate shelf off Texas (Parker, 1960). A com-
parison of the common animals from these three regions shows an almost
identical generic composition, which substantiates Thorson's (1951)
concept of parallel communities. For instance, in the check list of common
invertebrates for this environment (2 to 24 meters) off the Mississippi
Delta, 8 of the 1 1 gastropod species have their exact counterparts (even
to subgenus) in the nearshore, 11 to 26 meter environment in the Gulf of
California. Fifteen of the 22 pelecypods, all of the echinoderms, and a large
number of crustaceans are also represented by closely related species.
Most of these twin species were found too in the same depths and bottom
type off Texas. There was no doubt as to similarity of the assemblages
between the Gulf of California and Gulf of Mexico, although it is surprising
that no exact generic counterparts have been described previously, since
this assemblage undoubtedly exists elsewhere in the world. Three other
regions have been studied in tropical latitudes, but the environmental
factors are much more extreme and variable than those in the Gulf of
California. These are Madras, India in the Bay of Bengal, the Persian
Gulf, and off Ghana, West Africa. None of these regions was characterized
by the diversity of animals found in the American Gulfs, nor was there
much similarity in the dominant groups. However, the fluctuation of envi-
ronmental parameters in these regions, undoubtedly contributes to less
diversity.

Samuel (1944) published a few observations on benthic communities
in similar depths off Madras, India. She found that the primitive chordate,
Branchiostoma, was the most abundant animal on sand bottom between
18 and 30 meters. Two echinoids, including Lovenia (which also occurs
in the same environment in the Gulf of California) were the next most
abundant animals. Only two mollusks, a Marginella and Glycymeris were
common. No others were taken more than once. Except for the presence
of Lovenia, there seems to be little resemblance between the Madras
community and the one found at similar depths and on the same sediment
in the Gulfs of California and Mexico. A slightly different community
was found on clay bottom in these depths off Madras. An Anomuran crab
and several other decapod crustaceans were the dominant animals. The
only common mollusks were the gastropods, Oliva, Cantharus and Murex,
which were also found at similar depths in both Gulfs, but occupied no
position of importance within the community.

Thorson (1957) mentioned several communities from the Persian Gulf,
in depths ranging from two to 60 meters on sand and shelly sand bottom.
Only the dominants were given, none of which corresponded to the
dominants of the American communities or assemblages at these depths.

104

This is not surprising, as the Persian Gulf is noted for it's extremely high
temperatures and also hypersalinity. These extremes may be limiting to
a large number of invertebrate species. One community on shell gravel
was characterized by a species of Branchiostoma (thus parallelling Samuel's
community off Madras), a species of Venus, a Glycymeris and a polychaete,
Temnopleurus. A Branchiostoma community may exist in the Gulf of
California from preliminary observations, but was not sampled. The only
other community described by Thorson from the Persian Gulf in shallow
depths and on sand bottom was the Xenopthalmus pinnotheroides crab
community. The community was completely dominated by this small
crab, accompanied by a few polychaetes of no quantitative significance.
Apparently, there was nothing like the diversity of species found in the
Gulf of California in either the Persian Gulf or Bay of Bengal.

Buchanan (1958, p. 21-23) describes an "inshore fine sand community"
from depths of six to 15 meters off Accra, Ghana on the West African
coast. In overall aspect, the fine sand community was characterized by
two animals, the pelecypod, Cultellus tenuis (related to Ensis), and the
polychaete worm, Diopatra neopolitana. Within the major structure of
this community, three smaller communities were found which he called:
(1) the Owenia beds, (2) the Accra Bay silt patch {Macoma bed), and (3) the
Dentalium zone. The distribution of these small communities within the
six to 15 meter depths off Accra is reproduced in fig. 28. This picture is
quite similar to that shown in fig. 16 for the pattern of distribution of the
computor-designated groups of species in similar depths in the Tiburon
region. Buchanan attributed much of the patchiness of these communities
to small differences in grain size, organic matter content, and possibly
wave action. However, he found that there was nothing to distinguish the
environment of the Owenia beds from the rest, unless larval settlement of
the dominants had been influenced by the direction of the prevailing
current. Similar invertebrate species are also found in the Tiburon near-
shore sand bottoms, such as Ensis, Tagelus, several species of Tellina and
Macoma, and many tube-forming polychaetes, not yet identified. There
are minute differences in sediment types in this area, even though sands
predominate throughout (fig. 8). The group "7" assemblage, using Laevi-
cardium elenense as the key species, seems to be confined more to the
silty-sand portion of this environment, while the Chlamys circularis group
is more closely allied with shell-sand and shell-gravel sediments at slightly
greater depths. Mollusks were the typical components of these groups,
with pelecypods outnumbering the gastropods. The other index groups
contained more gastropods or crustaceans. The minute differences of
environmental factors within the major environments have yet to be

105

"^^^^^^^^fe^^

CRI5TIANSB0RG

NAUTICAL MILE'

Fig. 28. Illustration of the patchiness of community distribution in the nearshore "fine sand"
community off Accra, Ghana, from Buchanan (1958).

Studied in detail, especially where salinities, temperatures, and bottom
types appear fairly uniform. It is possible that here the biological factors,
such as competition, feeding types, larval development, etc. are more
important in limiting the composition of small communities than the
physical-chemical factors.

The nearshore, 11 to 26 meter region, with its almost uniform sand
bottom, provided an opportunity to check the effectiveness of the grab
sampler as opposed to the shell dredge in appraising the quantitative
aspect of bottom communities. As mentioned previously, the depths of
between 11 to 26 meters appear to be the most prolific in species of all
environments studied in the Gulf of California, resembling somewhat the
Venus community of British and Danish waters (Ford, 1923). Whether
this diversity compares quantitatively with other regions in the world

106

remains to be investigated in detail. It was possible to obtain some
quantitative figures for the nearshore sand bottom environment from eight
stations taken with a 1/20 m- Van Veen grab which only totaled 2 5 m-,
insufficient for strict square meter comparisons with other regions. An
average of 2.6 living individuals and 2.1 living species of animals was taken
from these eight samples using a 1 mm. diameter screen. Most of the
stations were taken in the southern Gulf, and the data for these stations
can be found in the appendix. The results of this survey are shown in a
table below.

Station
Number

1

8

9
16
21
22
24
26

Number Living

Number Dead

Number Living

Species

Species

Individuals

0

22

0

4

20

4

3

38

3

3

5

3

0

0

0

2

9

2

3

18

4

2

0

4

rage 2.1 /station

14/station

2.6'Station
or 52/m2

Five 1/10 m^ Petersen Grab samples were taken in one spot, within this
same environment, off Topolabompo near Los Mochis. Table VII gives
one an idea of how diverse this region is in respect to species, and also the
relatively low standing crop of animals which was found. These five samples
may offer the only valid comparison in this study with other benthic
studies, although the total area is still less than one half a meter. In-
spection of the species composition of these stations (Table VII) indicate
that they represent a rather good Tellina community, similar to those
described by Thorson (1957). Cumulative curves of these five samples,
as well as cumulative species curves for the eight Van Veen samples listed
above are given in fig. 29. These cumulative curves are based upon the
appearances of new species in successive samples as the area is also in-
creased. Fig. 29A gives first the cumulative curves for the eight samples
listed above in the 11 to 36 meter depth ranges, and secondly the curve
for equal-sized samples taken in the 1 to 10 meter depths. One can easily
see that the diversity is about the same in both environments. Fig. 29 b
gives the cumulative curve for nine nearly successive shell dredge samples
in the same region, also as area is increased. Both in 29 A and 29 B, plots
of the total number of species taken in each sample is given, in order to
demonstrate the relative uniformity of catch effort. Finally, in fig. 29 D,

107

le

A.

IE
K

f/

> 12

a 10

/^

o

AV

-/ ^' l-IOm sand flats

o '

/ / ll-36m nearshore shelf

/ / total number of species.

£ «

' t. 1-10 m sand flats

i 2

/ ■•• \ ....-•-■-.,.,

' , . T' .

'/20 '/lO 3/20 '/S '/« V|o V20 2/5 ,„2

TOTAL AREA m^

150

cumulative curve of different

new species

B.

130

total number of spedes

per station /

/'

120

/

110

/

wlOO
^ 90

^80

1

£60

J

i50

J \ / \

40

X / V '

30

^^

\

20

K^ ,.•■» I

•

10

J *

20 40 60 80 100 120 140 160
TOTAL AREA m2

180 m2

,4

cumulat

ve live mollusk

species

c.

13

total m

Husk species at

each s

at ion

12

^^

u, 10

^^

^ 9
0 8

/

y

/\

° 6

cr

/

3
2

/

<..^

...-

1
0

'/lO

'/5

3/10 2/5

'/? IT

2 TOTAL

P-51 A

B

C D

E

AREA

70

D.

60

aj Petersen and Boysen

Jensen (1911 J. First 20 stations w

,n 1/10 mZ

Petersen Gra

b ThisteO Bredning 14 27m.

t 50

b) Holme ( 19531- 20 statio

ns witn '/20m2 Scoop Sampler, W

tiitsano flay 16.5m.

-^

a *o

3)

a. 30

_^^b,

0
20

^^^-^

10

j-'--^

- -^

0 ■•

. . . . 1 1 1 .

0 5

1 0 15
TOTAL AREA m^

2 0m2

Fig. 29. Cumulative curves of appearances of new species in successive samples from various
localities in the Gulf of California and northwestern Europe.

A. Curves of 1/20 m- van Veen samples in two shallow environments in the southern Gulf
of California region.

B. Curve of 9 successive samples from the northern shelf region, taken with a small shell
dredge, covering roughly 20 m^ per sample.

C. Curve of mollusk species only from 5 equal-sized samples in one spot off Topalobompo,
Mexico, in a depth of 17 meters, using a 1/10 m^ Petersen Grab.

D. Cumulative curves of species diversity in 20 consecutive stations each from a) Denmark
and b) England.

cumulative curves for successive samples in boreal waters are reproduced
from Holme (1953) for Whitsand Bay, England, and from Petersen
and Boysen Jensen (1911) from Danish waters. There is no doubt con-
cerning the great diversity of Gulf of California waters as compared to
boreal waters when comparing this series of graphs. All of the Gulf of
California curves reach toward the asymptote, with little indication of

108

Table VII.
Analysis of numbers of individuals and species of living and dead in-
vertebrates from five successive Petersen Grab samples at Station P51,
depth 16 meters, fine sand bottom.

Species

Samples

C.

Oliva incrassata

Nassarius pagodus

Architectonica placentalis

Natica caneloenensis

Terebra malonei

Phos articulatus

Eulima varians

Balchis, sp

Pyramidella conica

Terebra variegata

Polinices intemerata

Philine, sp

Nuculana, sp

Chione mariae

Corbula, sp

Tellina felix

Lucina approximata

Pilar concinnus

Pandora, sp. (juv.)

Periploma, sp. (juv.)

Chione, sp. (juv.)

Tagelus politus

Anadara perlabiata

Corbula luteola

Cyclinella, sp

polychaetes

Total species living

Total species dead

Total individuals, living.
Total individuals, dead .

/ = living
1 = dead

5 +

/
1
1

6
2
1
/,3
/
7
/

5 +

5 +

6

6

10

14

2, 10

/,3

5 +

4

3

9

20

5 +

levelling off. On the other hand, both curves from boreal waters level off
after a few samples, and virtually no new species are added after the
fourth or fifth sample. Each new Gulf of California sample produces
nearly a whole new set of species.

109

The nine stations used in fig. 29 C were taken by a small shell dredge,
one half a meter wide, towed for five minutes at about one quarter of a
knot. This method covered about 20 square meters per sample, if the
dredge was kept constantly on the bottom. All samples were taken in the
Tiburon region in about the same environment as the eight grab samples
tabulated above. The overall catch was far greater with the shell dredge
than with the Van Veen, being at least ten times more productive in each
case, averaging 26 species and 87 individuals per station. Because the area
covered by the shell dredge was far greater than that for the grab samples,
an entirely different picture is obtained for the kind of animals living
there. If the shell dredge samples are equated on a square meter basis,
they produced only an average of 4.4 individuals per square meter, roughly
15 times less than that computed for the Van Veen samples. It would
seem, therefore, that the shell dredge is completely ineffective for quan-
titative studies, although it certainly produces a much greater variety
of animals, especially from groups seldom taken with bottom grabs (see
Thorson, 1957, pp. 473-476). The following table gives the figures for
the shell dredge catches.

Station
Number

178
181
183
184
190
194
195
196
208

Number Living

Number Dead

Number Living

Species

Species

Individuals

1

2

2

22

18

67

12

11

19

21

35

48

19

12

68

46

48

197

36

37

63

56

73

253

22

17

63

erage 26/station

28/station

87/station
or 4.4 m^

The figures for the number of identified species in the small dredge
samples gives some conception of how prolific this environment can be in
diversity of species, living and dead. The total average number of living
and dead species for all nine stations is 54 per station, while the greatest
number is 129. It should also be mentioned that many of the shells of spe-
cies recorded were those taken alive at other stations or in different years.
Although the majority of the Van Veen grab samples were taken to the
south of the shell dredge samples, two grab samples (Stations 24 and 26)
collected within the shell dredge sampling region, produced the same

110

number of species there as in the southern Gulf. Small trawl samples were
also taken in the southern section of this environment, and if anything,
the diversity of species was even greater than that produced by the shell
dredge. Although the species are not listed for the above two grab sample
stations, only one species was taken more than once, equalling the diversity
found in the grab sample survey of the shallow, sand-flat environment.
Either invertebrate distribution is extremely patchy on the continental
shelf of the Gulf of California, or each population of species is spread very
thinly over the bottom. Since the species composition is fairly similar in
the nine stations cited above, the latter alternative is probably the correct
one. Certainly, there is no apparent dominance of macro-invertebrate
species indicated here, similar to the boreal region studied by Petersen
(1911-1915), Thorson (1957) or Sanders (1956 and 1960) although such
a small bottom area was sampled quantitatively that valid comparisons
are impossible. Animals of the size studied by Sanders were not identified
in this study, although everything was saved which could be retained in
1 mm. screens. It was observed that relatively few polychaetes, amphipods
or copepods were collected from these sediment samples. This same lack
of dominance of any one species of invertebrate, large or small, was also
observed on the fine sandy bottoms of the northern Gulf of Mexico (Par-
ker, 1956a and 1960). Few quantitative benthic invertebrate studies have
been undertaken in the tropics and sub-tropics, with the exception of
Thorson's (1957 and personal communication) in the Persian Gulf (which
being hypersaline and very hot is on the whole a rigorous and unfavorable
environment), Buchanan's (1958) off Ghana, and Longhurst's (1957 and
1958) off Sierra Leone, Africa. For this reason it is difficult to make com-
parisons of standing crop and species diversity between the tropics and
the more well-known boreal regions. Sparck (1931) discussed the quan-
titative aspect of benthic populations as deduced from a small number of
samples in the Mediterranean. Although the waters sampled for this study
are generally warm, some of the species taken may also occur in Boreal
regions. Only a few very abundant species occurred in these samples,
paralleling the Danish communities of Petersen (1911-1915). Although
there seems to be no dominance of particular species of invertebrates in
the American sub-tropical regions, there is certainly dominance in the
Gold Coast area of West Africa (Buchanan, 1958) and off Sierra Leone
to the north (Longhurst, 1957 and 1958). In each of Buchanan's five
communities, lying roughly parallel to each other in descending depth,
there are about ten moderately abundant species, and at least one or two
very abundant species of invertebrates. No mention was made of the

ill

number of rare species taken at each station or the total number of species
occurring at any one station. Longhurst (1958) found no relationship
between the distribution of communities and depth, except for a change at
about 80 meters, with two communities inshore (a shelly-sand and mud
community), and one on the outer shelf and slope. The inshore com-
munities range into the estuaries and do not exactly correspond to any
of the Gulf of California communities. Relatively few species were given
in Longhurst's synopsis, but upon further appraisal of the discussions of
the various communities, there appears to be a much greater diversity.
There is no doubt, however, that both Buchanan's and Longhurst's
communities have a structure similar to those of Petersen, Thorson and
Sanders. The question then arises, how are the Ghana, Sierra Leone and
Persian Gulf regions different from the Gulf of Mexico and Gulf of Cali-
fornia, the former being characterized by a group of dominant animals,
and the latter, though having no dominant species, seems nevertheless to
have similar physical conditions? At least they are more similar to each
other in mean temperatures, than they are to Danish or Massachusetts
waters. The most important difference is probably in the extreme of
physical factors.

This lack of species dominance in the American waters, may well have
several explanations, both geological and biological. The great diversity
of level-bottom species in the tropical and sub-tropical Americas has not
been confined to Recent geological times. Dall (1890b- 1903) described
a large number of molluscan species from what is at present called the
Pliocene of Florida, and 312 species of mollusks from a small horizon in
the Miocene of Tampa, Florida (Dall, 1915). Similar very large lists of
mollusk species have been described from other Tertiary deposits in
North and South America (Gardner, 1926-1947; Woodring, 1925, 1928,
1957 and 1959; and Olsson, 1922). It is difficult to determine from fossil
deposits how many species may have been living at any one time in one
spot, but it cannot be denied that there was as much diversity in the
molluscan fauna during the middle and late Tertiary as there is today
in the warmer waters of the Americas. On the other hand, a check of the
molluscan fauna of the Middle Atlantic Miocene (Dall, 1904) or Danish
Miocene (Sorgenfrei, 1958), which were warm temperate to Boreal in
climate, shows a very small number of species as compared to tropical
Miocene formations.

Although there was a great diversity of marine mollusks in the northern
Gulf of Mexico (over 1,000 species on level-bottoms), the diversity is far
greater in the Gulf of California, where at least 1 ,400 level-bottom species

112

are known (Keen, 1958), and possibly another 1,500 are yet to be de-
scribed. One explanation for the great variety of mollusks within the Gulf
of California may be found within its geological history. In middle Tertiary
times, the relatively deep marine connections between the Caribbean Sea
and Pacific Ocean permitted a mixing of the two faunas, the greater part
of the migration taking place from east to west (Ekman, 1953). A large
number of new species were added to an already abundant, partly endemic
eastern Pacific fauna from the Caribbean. There has also been a continual
renewal of species from the Indo-Pacific region. Many western and southern
Pacific species are transported first to islands such as the Galapagos, Cocos
and Clipperton Islands, and eventually to the mainland (Rosenblatt,
1959; and Walker, 1960). During the Pleistocene, it seems that there was
also a southern migration of some California province species. Aside from
this recruitment of species from outside, the evolution of new species has
also certainly occurred. With the high primary productivity of the Gulf
as a basis for high benthic production plus the great variety of habitats
available for moUusk species, virtually all species from these various
zoogeographic regions can be successfully maintained in various parts of
the Gulf. Since no very drastic seasonal environmental changes occur, and
salinities remain constant and optimum for marine animals, most species
may only be eliminated by predation or competition for food. Sparck
(1926) suggested that both water temperature and availability of food may
affect the diversity and abundance of marine populations, although this
was implied indirectly. Through a series of tank experiments, Sparck
showed that a lack of food would tend to eliminate a large number of
invertebrate species growing and reproducing in cold waters, especially
those with high metabolic requirements. When the food supply was
reduced, only those with low energy requirements would remain, and these
could then become the dominant organisms in the environment. On the
other hand, a lack of food in warm (20" C.) waters had little affect on most
of the species adapted to these waters, since their metabolism would be
lower, and thus would need less food to survive. The population would
then consist of many species with relatively few individuals of each species.
There is yet another theoretical explanation for lack of dominance in
most of the Gulf of California assemblages. The majority of mollusks, and
perhaps other invertebrates, may have a very short life span of one to two
years, leading to an alternation of species in any one spot. During the
course of a year, one group of invertebrate larvae may settle in a particular
part of an environment, live and reproduce there, while the larvae of this
generation may settle elsewhere (see Thorson, 1950). The adults may also

113

prey upon the larvae of their own kind as they settle if the population of
adults is dense enough (Ursin, 1960). The parents may die in a relatively
short time, and a new group of species may then re-occupy the habitat of
the first group. One observation substantiating this surmise is that on the
shallow, sandy bottoms from 11 to 26 meters, there is one very large
assemblage of both living and dead moUusks, occurring either living or
dead at most of the stations. One group of stations may contain a number
of living species found only at these stations, although these same species
may also be found dead at another group of stations. The latter stations
in turn contain a different set of living species, which may be found dead
among the living population of the first set of stations. One argument
against this premise, is that environmental conditions seem to be very
uniform throughout the area where the 11 to 26 meter assemblage is
found. Salinities are constant, sediment-size is relatively uniform, and
temperature variations are not too great at these depths. If the environ-
mental conditions are constant, then larval settlement should be more or
less random and periodical. The strong tidal currents, which sweep back
and forth between the northern and central Gulf constitutes one factor
which does not remain uniform. If larval settlement should take place
when the currents are sweeping north, certain species may tend to settle
only in the northern part of the environment. Alternatively, if larvae are
produced during the southern trend of the tidal currents, settlement may
only take place to the south although these intervals may be too short
to be effective.

Of the 21 species of mollusks which were significantly found together
in this environment (Table IV), 12 species or 577o are suspension feeders,
4 or 20"/o are predators, 3 or 14^0 are deposit feeders, and 2 or 97o are
believed to be scavengers. As could be predicted in this environment, the
abundant animals (qualitatively) are suspension feeders, well-adapted to
the hard sand substratum which contains relatively little interstitial
organic matter. A preliminary analysis of probable feeding types for all
of the living mollusks taken at the computor-paired stations (fig. 17)
gave the following organization: 40 species or 45°/o are suspension feeders,
26 species or 30°/q are predators, 17 or 19°/o are deposit feeders, 4 or
approximately 4''/o are algae feeders, and 2 or about 2^0 are possibly
parasitic or commensal. These percentages are not too meaningful, since
the samples were not quantitative. Again the suspension feeders predom-
inate. The fact that intensive upwelling takes place nearby and occasionally
high inshore surface productivity (fig. 10) occurs in this area where these
typical stations were taken (fig. 17), may also account for the high per-

8 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126.

114

centage of suspension feeders, which could take advantage of these plank-
ton blooms. Analyses of feeding types of the dominant members of benthic
communities has seldom been attempted, although Sanders has done so
in both Long Island Sound (Sanders, 1956) and in Buzzards Bay, Massa-
chusetts (Sanders, 1958, 1960), and apparently by Savilov (1961) and
TuRPAEVA (1957), which were not available in their entirety to this author.
For instance, in Buzzards Bay, Sanders (1960) indicates that in the silty-
clay, Nephthys incisa-Nucula proxima community, the most abundant
three species are selective and non-selective deposit feeders, the fourth
ranked species is probably a carnivore, and the fifth a suspension feeder.
Of the 30 most abundant (by number, but not necessarily by weight)
species of invertebrates in this community, 10 or SS^/o are selective deposit
feeders, 8 or 26% are non-selective deposit feeders, 4 or 14% are suspension
feeders, 6 or 20% are carnivores, and the remaining V'/,, are scavengers and
one specialized deposit feeder {Turbunilla). Earlier, Sanders (1958) re-
marked that in Buzzards Bay, 80 to 99% by number of benthic fauna
comprised the primary consumers, i.e. herbivores and detritus feeders.
The filter or suspension feeders made up the majority of the fauna of sandy
sediments, while deposit feeders dominated the fauna on clay bottom. In
the sand-bottom Ampelisca community, suspension feeders constituted
two-thirds of the population by number, while 80% of the fauna of the
silty clay, Nephthys- Niiciila community are deposit feeders. This same
relationship between fine sediments and feeding types was also found by
Sanders to exist in Long Island Sound (Sanders, 1956, 1958). Sanders
results are therefore in relatively close agreement with those found in the
present study for the shallow waters of the Gulf of California. McNulty,
Work and Moore (1962), in a study of level bottom communities of south
Florida in somewhat comparable depths, but carbonate rather than
terrigenous sediments, offered several generalizations regarding the
relationship between feeding type and sediment size. Since terminology
differs from that used here, direct comparisons are difficult. They found
that detritus feeders predominate in the finest sediments, and deposit
and filter feeders at intermediate size grades. However, their sediment data
indicates that on the whole, grain size is much larger in Biscayne Bay,
Florida than in the nearshore environments of the Gulf of Mexico.

Two thirds of the index or characteristic 21 species for this environment
most likely have planktonic larval development, while the other third
could have non-planktonic development. Since nothing was known con-
cerning the exact reproduction of many of the Gulf of California species
of mollusks under discussion, larval development types were often hypo-

115

thesized from what was found in the literature concerning closely-related
sub-tropical and tropical species. It must be realized, however, that it is
known that development can differ radically within the same genus of
mollusks. For this reason, 40 species of important lamellibranchs were
examined by the author and W. K. Okkleman as to prodissoconch type.

V. Intermediate Shelf, 27 to 65 Meters:

The assemblage characterizing this environment actually becomes im-
portant as a distinct entity at about a depth of 39 meters, especially in the
southern Gulf. In the northern Gulf, the change is more gradual. Although
10 stations were taken in depths of 27 to 38 meters, only 38 species were
found, none being confined to these depths. Nineteen of these species
were more abundant in the shallower waters, while 19 were more com-
monly taken in the deeper waters. This overlap in depth ranges plus the
lack of large numbers of individuals and species indicates that there is a
transition zone between the major assemblages of the nearshore and
intermediate shelf depths. This transition zone was more distinct in the
southern Gulf, as the sediments were much finer than those inshore or
offshore, ranging from silty sand to silty clay. Reduced wave action
permits the accumulation of finer sediments along with greater amounts
of organic matter within the sediments. The larger amounts of organic
matter can apparently support a large population of Penaeid shrimp,
since the 27 to 38 meter depth zone is the primary inshore shrimp grounds
for both the Gulfs of Mexico and California. The shrimp and the more
common invertebrates found at these 10 stations, the echinoid, Lovenia
cordiformis, the scaphopod, Cadulus perpusillus, and the pelecypod,
Nuculana elenensis, are all deposit feeders, well adapted to feeding in this
habitat.

This same transition zone was also observed in the northern Gulf of
Mexico, wherever fine sediments occurred inshore of major sand bottom
areas resulting from lowered sea level (Parker, 1960; and Curray, I960).
As in the Gulf of California, the northern Gulf of Mexico intermediate
shelf assemblage was most distinct in depths of 39 to 65 meters on the
relict sand deposits. Only off Texas where deposition has been more rapid,
and fine sediments occur uninterrupted across the shelf, was the inter-
mediate shelf assemblage continuous from 20 to 65 meters. The assemblage
in this clayey zone in the Gulf of Mexico was also characterized by un-
common and widely-dispersed deposit feeders. The number of living
animals in 1/5 m- Van Veen samples from this transition environment off
Rockport, Texas averaged only 2.2 individuals per station or about 12

116

per square meter (Parker, 1960, p. 326). Five Van Veen (1/20 m^) samples
were also taken at the same depths in clayey sediments in the Gulf of
California. They averaged 6.3 individuals per sample, or 126 animals per
square meter, a much higher population than for the equivalent environ-
ment in the Gulf of Mexico. This may not be a valid comparison, as the
total area sampled this way was so small. These higher numbers might be
representative for the Gulf of California, since this zone is very narrow,
receiving a steady influx of animals from inshore and offshore. In the Gulf
of Mexico this zone is 10 to 20 miles wide, receiving little recruitment from
the other zones, at least in the central portion.

Buchanan (1958) also found a benthic community in more or less
equivalent depths of from 8 to 20 fathoms (15 to 36 meters) off Ghana,
which he called the "sandy-silt community". His community bears little
resemblance to the association of animals found in this study, except for
the presence of Penaeus duoarum, one of the dominant shrimp in the
inshore shrimp grounds (Hildebrand, 1954) on the coast of the northern
Gulf of Mexico. He also found very large populations of living and dead
Turritella annulata Kiener. This genus did not appear in abundance alive,
either in the Gulf of Mexico or Gulf of California. The dominant mollusks
of Buchanan's sandy-silt community were also deposit feeders, although
the dominant gastropod is a herbivore, which was said to feed on the algae
growing on the Turritella shells.

As indicated by a prolific and indicative fauna, the waters in depths
ranging from 39 to 65 meters constitute the most distinct portion of this
environment. However, many of the species found there still range into
shallower water, and dead shells can often be found along the shore. In
the previous description of the assemblages, the fauna of this zone was
divided into a northern and southern portion. The northern assemblage
was taken on sand bottom, while the southern assemblage is more con-
fined to clayey bottom. The northern assemblage, as revealed by the
computor associated stations was found exclusively on sand bottom re-
sulting from reworked old delta deposits presumably laid down during
lowered sea level and more pluvial periods (van Andel, etal., in press).
This assemblage and its equivalent on sand bottom to the south of San
Bias are remarkably similar to that found on relict delta sand deposits
off the Texas coast in 36 to 63 meters (20 to 35 fathoms) (Parker, 1960,
pp. 322-23). Again many of the mollusks from this environment are re-
presented by twin species from both oceans, which probably had common
origins in the Miocene and Pliocene shallow seas across Middle America.
A few of the Gulf of Mexico species of mollusks and their equivalents from
the Gulf of California intermediate shelf are listed below.

117

Gulf of Mexico

Scaphopods
Dentalium gouldii
Cadulus carolinensis

Gastropods
Calyptraea centralis
Natica floridana
Strombus alatus
Semicassis granulatus
Ficus carolae

Murex recurvirostris rubidus
Nassarius ambiguus

Pelecypods
Chlamys gibbus gibbus
Pecten ravenelli
Crassatella speciosa
Crassinella martinicensis
Liicina sombrerensis
Trigoniocardia media
Papyridea soleniformis
Laevicardium laevigatum
Microcardium tinctum
Gouldia cerina
Chione clenchi
Tellina tayloriana
Tellina lintea
Tellina squamifera
Macoma extenuata
Solecurius cumingianus

Gulf of California

Scaphopods
Dentalium oerstedii
Cadulus perpusillus

Gastropods
Calyptraea mamillaris
Natica idiopoma
Strombus gracilior
Semicassis centriquadrata
Ficus ventricosa
Murex r. recurvirostris
Nassarius pagodus

Pelecypods
Chlamys circularis
Pecten vogdesi
Crassatella gibbosa
Crassinella pacifica
Lucina excavata
Trigoniocardia biangulata
Papyridea aspersa
Laevicardium elatum
Microcardium pazianum
Gouldia calif ornica
Chione mariae
Tellina inaequistriata
Tellina reclusa
Tellina fluctigera
Macoma siliqua
Solecurtus guaymasensis

There are many more mollusks and other invertebrate species in this
environment in both gulfs, which are identical in appearance, and which
give similar aspects to both areas. The geological occurrences of most of
the pelecypods taken in the Gulf of California in this study can be found
in Olsson (1961). A surprising number of the species were found to occur
in middle Tertiary formations. Likewise, the twins of these species in the
Gulf of Mexico or their precursors have also been described from Tertiary
deposits of Florida (Dall, 1890b-1903) and the Caribbean (Woodring,
1925, 1928). Many of these twin species have identical depth, temperature
and sediment "preferences" today in both oceans. It is therefore possible
that large portions of the Central and South American Mio-Pliocene
seaways may have been represented by sand bottom at about these depths.
Here then, is another instance of the importance of the geological setting
influencing the composition of assemblages or communities. Tectonic

118

events during the Tertiary of Middle America furnished the setting for the
recruitment of this multitude of Caribbean species into Pacific coastal
community complexes.

Buchanan (1958) describes a community in similar depths off Accra,
Ghana which he terms the "silty-sand community", occurring in from
36 to 45 meters (20-25 fathoms). This community is characterized by a
giant Foraminifera, which so far has not appeared in shallow water in the
eastern Pacific. The only important molluscan species were a Cardium
and a Phos, while the crustaceans consisted of several species of decapod
shrimp. Most of the macro-invertebrate species also ranged into the off-
shore "coarse-sand community" to depths of about 90 meters (50 fathoms).
As can be seen, the kinds of animals in Buchanan's community bear
little resemblance to those found in equivalent depths in the Gulf of Mexico
or Gulf of California although water temperatures are slightly lower off
Ghana. Longhurst (1958) in his discussion of benthic communities off
Sierra Leone, West Africa gives no list of invertebrates restricted to inter-
mediate shelf depths, but rather finds strict dependence upon sediment
size and estuarine influence. It is evident from his data, that relatively
few invertebrate species live in depths of 27 to 65 meters compared to the
number of species living in similar depths in the Gulf of California. In a
discussion of the quantitative aspects of his study, Longhurst (1957)
did find that there was a decrease in number of species and individuals
with increasing depths. He also stated that there was little difference
between his region and similar depths in temperate, boreal and Arctic
waters in terms of the biomass, and individuals and species per square
meter. He reported that 800 species of animals were taken by grab and
dredge off Sierra Leone, which differed only slightly from Jones (1951)
list of 757 species from the Isle of Man in the British Isles, although com-
parisons of this sort are not too meaningful as the level of systematic
knowledge of the two areas are quite different.

Almost equal numbers of suspension, deposit and carnivorous feeders
were produced from a preliminary analysis of the feeding types of the
mollusks and a few other invertebrates found in the northern sand-bottom,
intermediate shelf assemblage. Of the 68 species selected for his survey,
17 are probably deposit feeders, 16 are suspension feeders, 15 are predators,
2 scavengers, 3 are algae feeders, and the rest are unknown as to feeding
habits. Although a sand bottom is usually characterized by an excess of
suspension feeders, these sands are at greater depths and less affected by
turbulence than most sandy areas, possibly allowing more organic matter
to accumulate on the bottom. The alternating strong currents which sweep

119

through the channel between Tiburon Island and the mainland, lose their
strength in the center of the distinct area confirmed by the matrix south
of Tiburon, and thus may begin to drop their load of silt and organic
material which become inter-bedded with the sand. Examination of the
prodissoconchs of the characteristic pelecypods from this environment
indicated that the majority of species have a pelagic larval development.

The second association within the intermediate shelf environment was
found in the southern Gulf. As in the northern region, nearly half (1 1 of 23)
of the index species from the matrix-associated stations proved to be
crustaceans. The principal environmental difference between the northern
and southern associations is that the majority of the 1 1 stations were
located on clayey bottom. Temperatures are much higher and have a
smaller range, thus permitting a larger number of tropical species to
survive there. Waters are also clearer and plankton blooms less common.

As in the northern region, the southern portion of the intermediate shelf
is characterized by a fauna with a strong resemblance to that found on the
intermediate shelf of the Gulf of Mexico (Parker, 1960, pp. 322-23). The
major difference between the two Gulfs is the fact that the genera con-
fined to clay bottom in the Gulf of Mexico are also found on sand bottom
in the southern portion of the Gulf of California. Many of the species on
the intermediate shelf of the Mazatlan region are also twins of the Gulf
of Mexico species found in similar ecological conditions. In fact, the
number of twin species is even greater in the southern than in the northern
Gulf of California. This is not surprising, since the ecological conditions
in the San Bias to Mazatlan region more closely resemble those of the
northwestern Gulf of Mexico shelf than those of the Tiburon region.

A survey of feeding types of the moUusks collected alive from the two
southern stations taken on sand bottom showed a predominance of pre-
dators and suspension feeders. Of the 61 species of mollusks taken alive at
these two stations, 34 are most likely predators, 15 are suspension feeders,
6 are probably deposit feeders, 4 algae feeders and 2 may be scavengers.
The feeding-type composition of the species is more normal for a sand
bottom than that found on equivalent sand bottoms in the northern region.
Eleven stations and 37 species of living mollusks were taken on clayey
bottoms in the southern Gulf. A breakdown of probable feeding types for
this assemblage produced: 12 suspension feeders, 17 predators, 6 possible
deposit feeders, and 2 probable algae feeders. The majority of the crusta-
ceans can also be considered as scavengers and predators. It was observed
that the species with the greatest number of individuals were the deposit
feeders. The large number of predators are accounted for by the fact

120

that most of the southern stations were taken with an otter trawl, the
best method for collecting the more mobile animals which comprise
most of the predators. According to a survey of prodissoconchs by the
author, most of the lamellibranch species have a planktotrophic larval
development. Perhaps 407o of the gastropods have a pelagic stage, but
it is almost impossible to be sure, since the gastropod survey was based
on probable development from related species. Thorson (personal com-
munication) states that within only a very few families of prosobranchs
is there strict uniformity in larval development. The high percentage of
species with pelagic development seems reasonable, since this environ-
ment in the southern Gulf is one of the largest in areal extent and
possibly the most uniform. Planktonic larvae should therefore settle with
a fairly high degree of success in this region.

VI. Outer Shelf, 66 to 120 Meters, Clay Bottom,
Southern Gulf:

The animals found on the outer shelf in the Gulf of California, especially
on clayey bottom, are very similar to those taken in equivalent depths in
the Gulf of Mexico. The large number of equivalent or twin species in this
environment, as in the previous one, suggest that clay bottoms to depths
of 100 meters may also have existed across Central and South America
during Tertiary periods. Of the 21 typical species taken in from 70 to 120
meters in the Gulf of Mexico (Parker, 1960), 13 had their exact equivalents
in the Gulf of California in the same depths, and an additional 6 species
were taken at slightly different depths. It is virtually impossible to separate
most of these "twin" species from the two gulfs without identifying labels.
One is also struck by the amazing similarity of trawl and dredge hauls
from the clayey bottoms of the two Gulfs. The twin species constitute the
largest populations, so that a preliminary appraisal of unlabelled samples
would give very little indication of which Gulf the samples originated
from. To demonstrate the close similarities of this assemblage in both gulfs,
a list of species from both areas is appended.

Gulf of Mexico (Parker, 1960, Gulf of California (Tables in

pp. 323^) 75-120 Meters Appendix) (40-65 Fathoms)

Pelecypods • Pelecypods

Anadara baughmani Hertlein, 1951 Anadara mazatlanica

Cuspidaria ornatissima (Orbigny, 1846) Cuspidaria pectinata

Eucrassatella speciosa (A. Adams, 1852) Eucrassatella gihbosa rudis (Crassatella)^

Laevicardium fiski Richards, 1954 No equivalent at this depth-

I

121

Lyropecten subnodosus (Linne, 1758)
Microcardium transversum Rehder

and Abbott, 1951
Nuculana jamaicensis (Orbigny, 1842)
Pecten papyraceus (Gabb, 1873)
Pilar cor data (Schwengel, 1951)
Poromya granulata Nyst and

Westendorp, 1839
Solecurtus sanctaemarthae (Orbigny, 1853)
Trigoniocardia media (Linne, 1758)
Verticordia ornata (Orbigny, 1846)

Gastropods
Conus clarki Rehder and Abbott, 1951
Distorsio mogyntyi Puffer and

Emerson, 1956
Muricopsis hexagona Lamarck, 1822
Polystira albida (Perry, 1811)

{— Pleuroliria)
Sconsia striata (Lamarck, 1816)
Turritella exoleta (Linne, 1758)

Echinoderms
Astropecten duplicatus Sladen

Crustaceans
Rhaninoides louisianense Rathbun

No equivalent at this depth^
Nemocardiumcentifilosum (Microcardium)

Nuculana laeviradius

No equivalent in eastern Pacific

Pitar catharius

Cyathodonta dubiosa?

Solecurtus broggii Pilsbry and
Olsson, 19411

No equivalent at this depth-
No equivalent at this depth^

Gastropods
Conus arcuatus

Distorsio constrictus
Ocenebra sloati

Pleuroliria oxytropis

No equivalent in eastern Pacific

No equivalent at this depth^

Echinoderms
Astropecten calif ornicus

Crustaceans

No equivalent at this depth^

1) These species were collected alive from this environment in a series of samples collected
by Joseph R. Curray in November, 1961. All were analyzed, but not included in computer
data.

^) The twin of the Gulf of Mexico species was taken in either slightly less or slightly greater
depths.

It is significant that the major offshore shrimp grounds (Hildebrand,
1954) are located on silty clay bottom in depths of 75 to 126 meters (40 to
65 fathoms) in both Gulfs. Preliminary observations of the shrimp grounds
in the Gulf of Thailand (J0RGEn Knudsen, personal communication) also
indicated about the same invertebrate composition for similar depths. In
all probability, shrimp (Penaeid) grounds in sub-tropical and tropical
regions throughout the world have a similar composition where the inverte-
brate genus or sub-genus is concerned.

Most of the lamellibranch species found on the clayey bottoms of the
outer shelf are thought to be deposit feeders or suspension feeders sub-
sisting upon organic material occurring close to the bottom. The majority
of the gastropods are predators. Those species which are not predators are
in the family Calyptraeidae, and are epifaunal in habitat. The feeding type

122

composition is therefore exactly as suspected for a deep water fine sediment
bottom and as found by Savilov (1961). The majority of the mollusks
examined from this habitat were found to have a pelagic larval develop-
ment, which would tend to produce a rather widely dispersed population
over this uniform environment.

VII. Outer Shelf, 66 to 120 Meters, Sand Bottom,
Northern Gulf:

Buchanan (1958) described an outer shelf community, designated as
the "offshore coarse sand community", which in terms of environmental
factors and faunal composition is quite similar to the Gulf of California
outer shelf sand bottom environment. While in the Gulf of California, the
sand-sized particles are mostly of terrigenous origin, Buchanan's coarse
sand deposits are calcareous in nature. Both sand deposits are probably
end results of the Holocene lowered sea level. Buchanan's characteristic
and abundant animals, a solitary coral, Caryophyllia, large numbers of
small tectibranchs, and another large Foraminifera, are either very rare
or not found at all in the equivalent Gulf of California environment. Some
of the rather scarce mollusks which Buchanan found in the coarse sand
community do have their equivalents in the Gulf of California at the same
depths. He found Eucrassatella, Phos, Cardium, two species of Corbula,
Nassarius, two species of Calliostoma, Pleuroliria, Pilar, Nuculana, and
a species of Pecten, all of which closely resemble the species of the same
genera found on the outer shelf of the Gulf of California. Temperatures for
these depths off Accra, Ghana are from 14° to 16°C. — about the same as
those for equal depths in the Gulf of California. Since both sediment type
and bottom temperature range are similar in depths of about 65 to 120
meters in both regions, it is not too surprising that there is such a similarity
of faunas as well.

No exact counterparts of this assemblage is known from other parts of
the world, since uniform terrigenous sand deposits are relatively uncom-
mon, except where deposition has been slow for a long time, and sands
remain uncovered at fairly great depths. The composition of the fauna
in this environment is very patchy (unlike the populations on the southern
clayey bottoms), and few mollusk species were taken more than twice
out of 18 stations. The crustaceans were by far the most abundant inverte-
brates and many were taken at four or five stations. Unfortunately, most
of the crustaceans were also collected at depths both offshore and inshore
of the outer shelf region, and thus are poor indicator species. In many
ways, the Tiburon outer shelf region is a transition area rather than a

123

distinct entity. The breakdown of the thermocline in this environment
because of intense turbulence and upwelling may contribute substantially
to the transitional nature of this assemblage. The majority of pelecypod
species are suspension feeders, while 80% of the living gastropods are
predators. A few of the gastropods species and about half of the lamelli-
branchs seem to have a pelagic larval development, which again is tran-
sitional in larval development types between shallow and deep waters.

VIII. Northern Gulf Basins and Troughs, 230 to 1,500 Meters:
No detailed studies have previously been carried out in any other region
with these peculiar environmental characteristics. Somewhat similar
environments may exist elsewhere, for instance the Red Sea, with its great
depths and warm bottom temperatures (21 to 23° C.) and high bottom
oxygen. However, apart from Fuchs' (1901) discussion of the "Pola"
expedition, the present author knows of no comprehensive study of the
fauna of the deeper parts of the Red Sea. Surprisingly, the benthic fauna
from 300 to 2,190 meters in the Red Sea was composed of typical bathyal
species resembling those found in the southern Gulf of California. Since
bottom temperatures are so high in the deep parts of the Red Sea, there
seems to be little reason for vertical stratification of animals. The lack of
at least some shallow-water species at these depths is also puzzling. One
also wonders how these typical bathyal species of invertebrates and fish
were able to cross the shallow entrance to the Red Sea from the Indian
Ocean. This may be one instance of pressure being a limiting factor to
distribution. Baldi (1961) has described a Miocene fauna from Hungary
which he presumes had lived in an environment similar to that found in
the Gulf of California northern basins and troughs. A few of the genera
reported by Baldi, such as Surcula, ''Gemmula'\ Amusium, a giant Den-
talium and Bathytoma ( ?) do occur at bathyal depths elsewhere and appear
to superficially resemble those mollusks taken at bathyal depths in the
Gulf of California. It may be hazardous, however, to state that Baldi's
Nassa-Pleurotoma clay represents the same environment as the northern
Gulf basins. More likely equivalents may appear in the Southern California
and Venezuelan Tertiary basins.

It is significant that none of the living species of mollusks from the
northern basins, and especially those from the 1,500 meter deep channels,
have ever been found as part of the lower bathyal or abyssal fauna else-
where. None of these species can be considered deep water species, the
majority having been found previously in shelf depths. Additional species
of mollusks were taken from the deep channels by Durham (1950) on the

124

"E.W. Scripps" cruise in 1941. The majority of Durham's collection con-
sisted of either new species (not taken alive) or were considered as fossils.
Even though the depths of these channels are thought of as abyssal, none
of the mollusk species collected in this or Durham's study were listed in
Clarke's (1962) tabulation of abyssal mollusks of the world.

The problem of explaining the presence of the Californian Province
mollusks, cited previously for the northern Gulf basins, is a difficult one,
although a hypothesis is presented here. Most of these cold, shallow-water
species were actually collected from several shelly-sand layers in large-
diameter piston cores which were taken from the center of Tiburon basin.
Present bottom water temperatures in this basin range from 11 to 14°C.
These temperatures are about the same as those found during most of the
year on the continental shelf off California. Some of these same species
were also collected as sub-fossils in between 200 and 800 meters off Cape
San Lucas, Baja California. It is possible that these cold, shallow-water
species of mollusks entered the Gulf of California around Cape San Lucas
during the colder parts of the Pleistocene and during lowered sea level.
A few shallow- water (although more tropical) species of shells were dredged
at the edge of the shelf off San Bias, Nayarit in 110-1 15 meters (62 fathoms).
These shells were dated by the C-14 method by George Bien of Scripps
Institution. They gave ages between 17,000 and 19,000 years B.P. (Curray,
1962). These dates furnish some proof that sea level was at least 100 meters
lower than at present in the Gulf of California. If the sea level were to be
lowered 100 meters in the Gulf of California at the present time, there
would be virtually no continental shelf up to Tiburon Island. However, a
shelf with depths of 15 to 150 meters would exist in the northern Gulf.
During early Holocene times, the northern Gulf would have provided the
primary environment for the settlement of any California shelf species
which might have invaded the Gulf during lowered sea level migrating
slowly northward on what narrow shelf areas that may have existed.
Since the northern Gulf deep-water bottom temperatures are now approx-
imately the same as those that might have existed in shallow-water during
the Pleistocene, and equal to those now present on the shelf off California,
a number of cold-water mollusk species could survive. The fact that some
of these cold-water species were taken alive during this study substantiates
this hypothesis. The majority of the Pleistocene populations perished,
contributing to the shelly deposits now buried under a few feet of recently-
deposited clay in the northern Gulf.

Owing to the peculiar physical conditions in the northern deep basins

125

and troughs, the analysis of the feeding types of the animals living in this
environment is of some interest. As there were so few living species col-
lected, it will be difficult to give a true assessment of the dominant feeding
types. All of the pelecypod species are deposit feeders, the single gastropod
is a predator, the two echinoids are non-selective deposit feeders, the three
scaphopods are deposit feeders and the eight coral species are probably
predaceous suspension feeders. The feeding types among the shallow-water
dead shell species found in the deep troughs consisted entirely of sus-
pension and algae feeders — the dominant feeding type found on the
intertidal rocky shores at the edges of these channels. The California
Province mollusks found as dead shell in the basins consisted of 80"/o
deposit feeders, and \2°/q were designated suspension feeders, giving some
indication that they must have lived in a detritus-rich clay bottom en-
vironment.

IX. Upper Slope, Central and Southern Gulf,
121 to 730 Meters:
The list of invertebrates for this environment is typical of bathyal
depths, and two species of mollusks found in this study, the pelecypod,
Nucula Cardura, and the scaphopod, Cadulus californicus, were even
reported from abyssal depths in a list of all known abyssal mollusks com-
piled by Clarke (1962). Bottom water temperatures in this portion of the
Gulf are normal for bathyal depths, ranging from 1 1° or 12°C. in the upper
parts to about 4° or 5°C. in the lower or deeper portions. Oxygen concen-
trations are very low at these depths in most of the Gulf (fig. 6), ranging
from 1 ml/L. in the shallower portions to less than .05 ml/L. in the 300
to 500 meter zone, increasing slightly to .5 ml/L. at depths of 700 to 800
meters. Very few living organisms were taken in the low-oxygen portions
of the upper slope, and several regions were completely devoid of life, even
though trawls and dredges brought up large amounts of wood and un-
decayed organic matter (Goldberg and Parker, 1960). The only animals
which could be considered at all common in this zone were several species
of Stomatopod shrimp (Squilla), and at times tremendous numbers of
Pleuroncodes planipes and Munida, both Galatheid shrimp. It is suspected
that all of these shrimp are probably carrion feeders and thus should find
food plentiful in this region where organic decay is very slow. It is of
interest that Vinogradov (1953) stated that both Squilla and Pleuroncodes
are high in phosphate content, especially in the form of the mineral,
apatite, the principal mineral found in phosphatized wood taken in this

126

environment (Goldberg and Parker, 1960). Not only is oxygen almost
non-existent in portions of the upper slope environment, but phosphate
concentrations are exceedingly high, reaching saturation point. This
correlation between high phosphate in the organisms and the environment
is therefore not too surprising.

Two other invertebrates were abundant in the upper portions of the
"oxygen-minimum" zone off Baja California in the Pacific Ocean, a
gastropod, Nassarius miser, and a holothurian, Cucumaria chilensis.
Pleuroncodes occurred in such abundance at these localities that they
created the effect of a red sea at night. Trawling beneath these large surface
concentrations of Pleuroncodes produced an abundance of casts and parti-
ally decayed individuals (Boyd, 1963). It is possible that the decay of these
tremendous populations of Galatheids depletes the oxygen in this zone
and also provides the organic matter for the large numbers of Nassarius
and holothurians on the bottom.

There are no comparable studies of the bathyal assemblage as a whole
in the literature, although bathyal invertebrates have been collected by
many expeditions and discussed in monographs for almost every phylum.
Dall (1886, 1889, 1890 and 1908) discussed at great lengths the mollusks
collected from both bathyal and abyssal depths along the Atlantic and
Pacific coast of the Americas. There are also many papers in existence on
other invertebrate groups from bathyal depths, resulting from the various
cruises of the American fisheries vessel, Albatross. It is too difficult, at
the moment, to attempt a compilation of all the species by station, in
order to determine the assemblages or communities found. This same draw-
back applies to the "Challenger", "Siboga" and other major deep sea
expeditions. Even Ekman's (1953) discussion of the bathyal fauna gives
little indication of the association of animals to be found. He also con-
fined his treatment to north Atlantic depths, where the fauna has little
resemblance to that found in tropical bathyal regions. Sparck (1951) took
several quantitative grab samples at lower bathyal to abyssal depths off
West Africa but did not list the species.

Even though the majority of the species of animals in this environment
are deposit feeders or scavengers (on the basis of anatomy), 26% of the
species can be classified as suspension feeders, a rather high percentage
for these depths. This relatively high percentage of suspension feeders
probably subsist on the rain of organic matter resulting from the high
primary production in the surface waters of this zone. The high primary
production on the surface seems to be one of the major causes of the
"oxygen-minimum" zone, since blooms are often found overlying strong

127

thermoclines, which often foUow a period of intense upwelHng. Dissolved
oxygen in the water column below the thermocline is rapidly depleted by
the oxidation of the organic debris (resulting from the death of the bloom)
as it falls to the bottom. Even so, much of the organic matter does reach
the bottom unchanged, thereby providing food for the detritus feeders
and scavengers living there.

Virtually nothing is known concerning the larval development and
reproduction of the mollusks living in the upper bathyal regions. A pre-
liminary examination of the prodissoconchs of some of the lamellibranchs
by W. K. OcKELMANN and the author indicated that at least some of them
have a lecithitrophic development and probably no pelagic veliger or
feeding stage. Ockelmann (1958 pp. 243-45) has shown that the number
of non-pelagic larval species of lamellibranchs increase rapidly from Boreal
to Arctic waters, while Thorson (1944) indicated that none of the species
of prosobranch gastropods investigated by him in the Arctic had a pelagic
development. According to a preliminary analysis of the Gulf of California
data, a similar phenomenon occurs in the Gulf where the number of species
of mollusks having a pelagic larval development decreases with increasing
depth. Similar observations were also reported by Thorson (1950, pp.
26-28). Since bottom water temperatures approach Arctic values as one
descends into abyssal depths, and food becomes less plentiful, it would
seem that temperature and availability of food may influence the distri-
bution of mollusk species with non-pelagic larval development.

X. Middle Continental Slope, 731 to 1,799 Meters:

The mid-slope assemblage is a typically deep-sea one, composed entirely
of lower bathyal and upper abyssal fauna. Three of the eight species of
mollusks taken in this environment were listed as abyssal by Clarke
(1962) and all of the genera are primarily abyssal in distribution. Bottom
water temperatures (3 to 6°C.) are partly in the abyssal range, according
to the description of the abyssal environment given by Madsen (1961).
There seems to be no real dividing line between abyssal and bathyal,
based on depth or temperature alone. Whether a fauna in any region is
bathyal or abyssal depends upon many circumstances. For instance, depth
is not a valid limiting factor, when one considers the fauna of the deep
isothermal basins, such as the Red Sea, Ballenas Channel in the Gulf of
California, and the Sulu Basin. These areas have what have been called
abyssal depths, but are characterized by high outer shelf temperatures at
the bottom. Likewise, the Arctic and Antarctic regions have abyssal

128

temperatures of 1° to 2°C., but in many places depths of much less than
2,000 meters. If depth or pressure were the determining factor, then
animals normally found in the middle continental slope environment depths
should also occur at similar depths in the northern basins of the Gulf of
California. On the contrary, a fauna of much shallower water but known
previously from equivalent bottom temperatures was found. If temper-
ature is the primary limiting factor, why do many of the Arctic and
Antarctic bottom faunas remain mostly near the poles? Relatively few
Arctic species are ever found on the abyssal sea bottom, south of 30°
north latitude, nor are Antarctic species found north of 30' south latitude,
even though bottom temperatures typical of shallow polar waters extend
over most of the abyssal sea floor.

No community or ecological studies concerned primarily with this
particular environment are known from the literature. Numerous col-
lections have been taken on the slope and many species have been de-
scribed from these depths, but as in the upper slope environment, a
synthesis of this material is difficult. The best descriptions of partial
assemblages of the middle continental slope environment can be found in
the narratives of the Challenger (Murray, 1895, and Moseley, 1880),
Albatross (Townsend, 1916), Siboga (Weber, 1902), Swedish
Albatross (Nybelin, 1951), and Galathea (Bruun, Greve and Sparck,
1956, and Madsen, 1961) Expeditions.

All but five of the mollusk species collected alive from this environment
are deposit feeders. The four octocorals may be considered suspension
feeders, although the term predator might be a better classification. No
attempt was made to classify the crustaceans as to feeding types, although
the shrimp living just off the bottom and the large decapod crabs are
probably predators or scavengers. The fact that some suspension feeders
exist at these relatively great depths is not too surprising, since surface
production is still rather high over this portion of the slope, at least along
the Middle American coast. No estimate can be given of the larval develop-
ment of the mollusks taken in this environment. Natland (1933) described
a Pliocene deep sea fauna from southern California Tertiary basins. A few
mollusk species related to those occurring in this assemblage have been
found in Miocene and Pliocene formations of the West Coast of North
America (Grant and Gale, 1931), and the Pliocene of Costa Rica and
Panama (Olsson, 1942), so that this assemblage may still have some use
in paleoecological interpretations, even though this environment is con-
sidered too deep for most geological formations containing abundant
fossil material.

129

XI. Abyssal Southern Borderland Basins and Outer
Continental Slope, 1,800 to 4,122 Meters:

This is not only the deepest of environments studied in the Gulf of
California and along the West Mexican coast, but it is also one of the most
fascinating especially with regard to the types of creatures living there.
The majority of deep-sea expeditions have concentrated on the more
accessible upper slope regions, or the true abyssal sea floor and deep
trenches. For instance, the Galathea Expedition (Bruun, 1959) con-
centrated on the deeper parts of the oceans, particularly the trenches and
the abyssal and hadal depths below 6,000 meters. The Russian expeditions,
using the Vityaz and Ob (Filatova, 1959; Zenkevitch, etai, 1959;
and Zenkevitch and Beljaev, 1955) also carried out most of their sam-
pling on the great abyssal plains or at hadal depths in the trenches. The
American Albatross concentrated more on slope than did any of the
other expeditions, since they were originally interested in marine resources
which were close enough to shore to be utilized by man.

Even though the lower portions of the continental slope off most con-
tinents are characterized by so-called abyssal depths and temperatures
(2,000 to 4,000 meters, and 1" to 2.5° C), the richness and complexity of
the faunas are not duplicated anywhere else in the deep sea, and in many
cases not even on the continental shelf. An example of the richness of
fauna from the continental slope region off Central America is given by
Wolff (1961) in a partial list of one trawl hawl taken off Panama and
Costa Rica. This was the richest deep sea haul ever made, although similar
rich hauls were taken with smaller gear by the present author off Mexico.
Several of these hauls produced almost as many individuals and were of
nearly the same composition as Galathea Station 716. For instance, two
3-meter Agassiz beam trawl hawls were taken during this study in from
2,000 to 4,000 meters off Baja California in June, 1961, and each contained
between 100 and 300 kilograms (200 to 600 pounds) of one species of
Macrourid fish alone. Plates XI-XV illustrate the benthic life in the re-
gion within a few miles of the Beam Trawl stations of the present study.
On the average, otter trawls taken on the lower slope off Mexico produced
much larger catches per hour on the bottom, than trawls taken with the
same gear in depths of 50 to 100 meters.

There are several reasons why the standing crop of benthic invertebrates
and probably vertebrates is so high on the lower continental slope and
borderland basins. One of these is that the slope is, morphologically,
closely associated with the continental land masses and thus still close
enough to shore to be affected by coastal surface productivity. Many of

9 \'idensk. Medd. fra Dansk naturh. Foren. Bd. 126.

130

the deep coastal basins are beneath major upweHing areas, with their
high surface production and associated great accummulation of bottom
organic matter. Continental shelves along the west coast of the Americas
are very narrow and, because the continental slope drops off very sharply,
numerous slumps and turbidity currents occur which transport shelf
organic debris to abyssal depths.

It was hypothesized by Parker (1961) that the competition and
evolution of many new forms during the early Tertiary forced many of
the older forms of animal life deeper down into the newly-formed trenches
and borderland basins which were as yet unoccupied by present-day
animal life. It is suspected that present day forms were absent from these
great depths at that time, because recent geological and geophysical
evidence suggests that many of the present deep ocean basins are rela-
tively young, and most of the major trenches of the world are thought to
have been formed only since early Tertiary times (Parker, 1961). The
major abyssal plains of the central Pacific are still comparatively devoid
of animal life (Filatova and Levenstein, 1961; and Agassiz, 1905),
which may also be related to the virtually barren surface waters over these
basins. The relative youth of the trenches is substantiated by the fact
that each trench seems to have its own endemic fauna (Zenkevitch and
BiRSTEiN, 1960), most of which have evolved either from Tertiary shallow
water forms, or have differentiated rather recently from older animals
which had already migrated on to the continental slope prior to the
Tertiary.

In Wolff's (1961) paper on the description of the animals from one
Galathea station (716) off Costa Rica in 3,570 meters depth, he lists
54 species of invertebrates. From a composite of stations taken in equiv-
alent depths between Baja California and Guatemala during this study,
86 invertebrate species have been identified (pages 186-87). A number of
faunal groups were identified in Wolff's paper, but were not identified
in this study and vice-versa. Although sponges, actinarians, polychaetes,
asteroids and ophiuroids (identified in Wolff's paper) were taken in
large numbers in this study, most have not yet been identified by specialists.
Likewise, Wolff has not yet received identifications for brachiopods and
soft corals which were identified in the present list. Only twelve species
of invertebrates were taken in common by both sampling programs, of
which five were mollusks, two pycnogonids, two holothurians, oneophiuroid
and two echinoids. Wolff reports one species of fish from Station 716
and indicates that other species were also taken. Fish were abundant in
the present samples, most of which have been identified by Carl L. Hubbs
and Richard Rosenblatt of Scripps Institution. Other descriptions of

131

abyssal fauna on a single catch basis can be found in Murray (1895),
Weber (1902), Nybelin (1951), Zenkevitch, etal. (1955), Bruun (1957),
SuYEHiRO, etal. (1960) and Wolff (1960).

As is to be expected, the majority of the species of animals living in the
abyssal borderland and slope environment are deposit feeders, most of
which are moUusks and echinoderms. Nothing is known concerning
reproduction of these species. Further research on deep sea animals should
now be concentrated on the biology of these animals, rather than zoo-
geography, but this will necesitate far more sophisticated sampling
techniques than are now available.

A check was made as to the abyssal character of the molluscan species
taken in this environment, by using Clarke's (1962) compilation of
abyssal mollusk records from the literature. Altogether, 27 species of
mollusks were identified from the lower slope and southern borderland.
Of these, 18 were listed as abyssal by Clarke. Those species not considered
new have also been taken in slightly shallower depths, but farther north,
and would still be considered abyssal on the basis of temperature. The
majority of the other invertebrates have been collected only in abyssal
depths, indicating the true abyssal character of this assemblage.

Surprisingly enough, elements of this same abyssal assemblage have
been reported from Pliocene sediments in Costa Rica, Panama and Ecuador
(Olsson, 1942). Typical abyssal and bathyal genera, sub-genera and
species of mollusks, directly related to forms taken in depths of between
500 and 3,000 meters on the adjacent slope were well-preserved in dark
shales and sandstones, which must have been uplifted several thousand
feet.

XII. California Borderland Basins, 1,641 to 2,358 Meters:

As mentioned previously, the differences in the fauna of the northern
basins along the California coast seem to be sufficient to constitute a
different assemblage, partly abyssal in nature. Of the mollusks found in
this environment, Clarke (1962) reports only 8 of the 25 species as being
abyssal. The rest have been reported as either bathyal or as Arctic shelf
species. It was also observed that most of the fish taken from the Cali-
fornia borderland region were either shallower water species or had pre-
viously been taken on the continental shelf of the northern and north-
western Pacific (HuBBS, personal communication).

It is puzzling as to why the California borderland basin assemblage is
so different from that found at equivalent depths to the south, since
temperature, oxygen and sediment conditions are similar in both areas.
The only feasible explanation for this separation of faunas is that the

9*

132

California basins (probably formed during the middle Tertiary [Emery,
I960]) have been occupied by a northern rather than a southern migration
of benthic animals. The Mexican basins and slope, on the other hand,
seem to have been occupied by a migration to the north from the Tropics.
Barriers separating the northern and southern borderland exist as shallow
ridges cutting transversely across the slope into Baja California (Krause,
1961 and in press). These ridges may serve to separate the migration of
animals from both directions. There is also some evidence from unpub-
lished deep current studies that the bottom waters along the coast of Cali-
fornia may move in a general southern direction, thus inhibiting larval
transport on the bottom from south to north. A thorough study of the
oceanography, geology and a summary of the biology of the Southern
California borderland basins can be found in Emery (1960). Hartman and
Barnard (1958) have written a more detailed study of the faunas of the
somewhat shallower borderland basins, which are quite different from those
studied in this paper. The inner basins have very shallow sills, which severe-
ly limit the bottom oxygen concentrations, thus benthic invertebrates are
often lacking or very scarce. None of the benthic species of invertebrates
found by Hartman and Barnard in the inshore basins were taken in this
present study, even though some of their samples were taken in over 1,000
meters.

An analysis of feeding types produced a predominance of deposit
feeders and scavengers, as should be expected at these depths. Of the
37 species of invertebrates identified and listed previously in the discussion
of the assemblages, 15 are deposit feeders, five probably scavengers,
14 are mobile predators, two are considered suspension feeders and one a
fixed predator. The feeding composition, then, is about the same as that
determined for the abyssal assemblage to the south. The majority of the
gastropods from this environment are Buccinids, which are known to have
direct development from egg capsules, and all but one of the lamellibranch
species seem to have a lecithitrophic or non-pelagic development as well.

Summary and Conclusions

The data obtained in this study have made it possible to describe some
of the major benthic invertebrate communities or assemblages on the
continental shelf of an unusual subtropical to tropical region and have also
provided information as to the composition of some deep sea assemblages.
Seldom before, has there been an opportunity to investigate the degree
of association between such a large number of species (1,150) and stations
(272) for such a great variety of marine environments. The existence of a

133

large body of data for a number of ecological factors has enabled the
author to explain some of the vagories of faunal distribution within this
interesting region, based both on the distribution of the abundant animals
and the boundaries of the physical-chemical factors. The biology (develop-
ment and feeding habits) of some of the components of these assemblages
has been superiicialiy investigated, offering a few more parameters to help
explain marine invertebrate distribution. Finally, various events in the
past (the geological factors) have afforded yet a few more explanations
for the "whys" of animal zoogeography.

In all, 12 distinct assemblages of benthic invertebrates, based on the
close association of the most numerous and characteristic species, and also
representing 12 environments or major habitats, were found in the area
included in this study. This region encompassed the west American coast
from San Francisco, California to Guatemala, and included the entire
Gulf of California. These 12 assemblages have a few abundant species but
were generally characterized by a great diversity of species and relatively
few individuals of any one species. The 12 environments which have
distinctive assemblages of invertebrates are:

I. Intertidal rocky shores.

II. Intertidal sand-beach and sand-flats to 10 meters.

III. Low-salinity lagoon and mangrove mud flats.

IV. Nearshore, sand and sand-mud bottom, 11 to 26 meters.
V. Intermediate shelf, 27 to 65 meters.

VI. Outer shelf, 66 to 120 meters, clay bottom, southern Gulf.

VII. Outer shelf, 66 to 120 meters, sand bottom, northern Gulf.

VIII. Northern Gulf basins and troughs, 230 to 1,500 meters.

IX. Upper slope, central and southern Gulf, 121 to 730 meters.

X. Middle continental slope, 731 to 1,799 meters.

XI. Abyssal southern borderland basins and outer continental slope,

1,800 to 4,122 meters (limits of sampling depths).

XII. California borderland basins, 1,641 to 2,358 meters.

Many of these environments and their assemblages have counterparts
in other parts of the world, although few benthic ecological studies have
been carried out in tropical and sub-tropical areas of comparable richness.
Those environments investigated elsewhere are: the intertidal rocky
shore; intertidal sand flats; low-salinity lagoons; nearshore shelf, inter-
mediate shelf, outer shelf on clay and sand bottom, upper slope, middle
slope and abyssal slope. Those with no exact known counterparts in the
world are: the northern Gulf basins and California borderland environ-

134

ments. A diagram illustrating the relationship of these assemblages to the
geomorphology of the sea bottom and surrounding land masses is shown
in fig. 27.

The average standing crop of benthic invertebrates for the inshore
assemblage appears low as compared to that found for quantitative studies
carried out in temperate or boreal regions. Since so few quantitative
studies have been made elsewhere in the tropics and the area covered
quantitatively in this study is so small, a comparison between the Gulf
of California and other tropical regions is difficult.

Evidence was produced from a comparison of shelf assemblages found
off the Pacific coast off Mexico and in the Gulf of Mexico that a large
number of twin or allopatric species of mollusks are present at certain
preferred depths and on specific sediment types. These almost indis-
tinguishable "twin" species are presumed to have descended from single
common species which moved freely between the Atlantic and Pacific
Oceans across submerged portions of Middle and South America during
Miocene and Pliocene times. Since the "twin" species now occupy exactly
the same environment on each side of the Middle American land mass, it is
hypothesized that the original Mio-Pliocene species also lived in similar
environments. This phenomenon is most evident in the intermediate shelf
sand bottom, 27 to 65 meters, and outer shelf, clay bottom, 66 to 126
meters environments. For this reason, it is suspected that at some time
the marine connections across Middle America must have been in depths
of at least 27 to 120 meters, with certain areas covered continuously with
sand and others with silty clay. Few "twin" species were found below
120 meters, although a number of cosmopolitan deep-water species were
taken at depths below 1,000 meters.

An analysis of feeding types (mostly of mollusks) for the various assem-
blages indicated a close relationship between feeding type and bottom
character, as well as other factors in the marine environment. In general,
a larger number of suspension feeders, along with an equally large number
of predators, are found on well-sorted sands and silts, especially in the
shallower waters. The deposit feeders and scavengers usually outnumbered
other types on poorly-sorted sandy mud and deeper silty clay sediments.
Certain areas below the euphotic zone were still occupied by fairly large
numbers of suspension feeders. These areas are also characterized by very
high surface plankton production and at times considerable turbulence.
These factors may allow suspension feeders to utilize as food, the suspended
organic matter resulting from the high surface production.

Finally, this study has produced a few more parameters for paleoeco-

135

logical interpretation, especially the deeper environments. These criteria
may be useful in interpreting the environments of deposition of ancient
basins and continental slopes. The living assemblages found both in the
shallow and deeper waters closely resemble those found in Tertiary deposits
around the Gulf of California, in Central America and in the Caribbean
region. The use of computer filing and analysis as used in this investigation
may facilitate the interpretation of modern as well as ancient environments.

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137

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143

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ocean. - Itogi Nauki Dost. Okeanol., 1 : 106-147 (in Russian).

Appendix: List of Stations

Stat.

Date

Time
from

+ 7
to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sed.
type

Device

1

2

3/59

1940

15

23° 12.8'

106°29.7'

15.0

3.0

1

57

2

7

3/59

1829

45

24° 18.0'

107°50.0'

15.0

3.0

75

52

3

8

3/59

0535

2710

23"58.4'

108°59.5'

2.0

2.0

72

82

4

10

3/59

2100

4

7

24° 13.5'

110°18.5'

22.0

3.0

59

5

13

3/59

1200

4

7

25°21.3'

108°51.7'

24.0

3.0

57

6

17

3/59

2133

68

26°32.2'

109°36.8'

12.0

3.0

59

7

22

3/59

1200

7

9

25°52.5'

109°27.5'

24.0

5.0

71

52 59

8

25

3/59

1109

23

27°06.0'

112°00.0'

22.0

4.0

57 59

9

26

3/59

1805

13

27°20.5'

11 2° 16.0'

22.0

3.0

59

10

30

3/59

1830

135

183

27°42.0'

112°37.5'

13.0

3.0

59

11

31

3/59

1425

11

27°46.4'

112°42.1'

22.0

4.0

59 57

12

31

3/59

1746

73

78

27°54.5'

112°45.2'

22.0

3.0

59

13

1

4/59

0245

33

28°25.0'

112°03.1'

11.0

3.0

59 57

14

1

4/59

0510

13

28°31.5'

1 1 1°54.0'

15.0

4.0

57

15

1

4/59

1455

13

28° 11.7'

112°48.2'

22.0

4.0

57

16

1

4/59

1645

22

28° 18.0'

112°52.0'

22.0

4.0

57

17

1

4/59

2142

31

28°43.5'

11 2° 18.0'

15.0

3.0

52 59

18

2

4/59

1954

402

28°51.0'

112°37.2'

12.0

3.0

51 59

19

2

4/59

2210

421

28°44.2'

112°48.5'

8.0

2.0

51

20

3

4/59

1430

735

28°08.1'

11 2° 16.0'

4.0

.5

52

21

5

4/59

1410

25

28°56.0'

113°33.8'

22.0

4.0

57 59

22

6

4/59

1145

13

29° 16.0'

113°17.0'

15.0

2.3

57 59

23

6

4/59

1707

92

29°32.7'

112°45.r

16.0

2.4

59

24

6

4/59

1855

23

29°39.2'

112°34.5'

16.0

2.5

57 59

25

8

4/59

0453

33

30° 19.3'

112°54.3'

19.0

4.0

51

26

8

4/59

2310

23

30°56.0'

11 3° 16.8'

20.0

4.7

75

57

27

9

4/59

0030

64

30°52.0'

113°26.0'

22.0

3.6

73

51

28

9

4/59

1020

25

30°05.2'

114°36.0'

21.0

3.3

1

51 57

29

10

4/59

1010

27

3r07.1'

114°38.2'

20.0

4.2

74

57 59

39

20

3/59

1710

1828

22°48.r

110°11.2'

2.0

2.0

4

77

40

21

3/59

2100

1340

366

22°48.2'

109°47.4'

2.3

2.5

77

63

41

22

3/59

0712

0845

2790

2817

22°32.2'

109°43.0'

1.5

2.0

72

74

42

26

3/59

0840

1400

2622

2715

22°35.6'

110°06.5'

1.5

2.0

72

74

43

27

3/59

0600

0700

366

212

22°48.0'

109°44.5'

11.0

1.0

5

78

44

27

3/59

1500

1630

366

512

22°51.5'

109°41.3'

10.0

.5

77

78

45

28

3/59

1131

1254

330

340

23°00.1'

109°35.7'

12.0

2.5

6

78

46

28

3/59

1745

1750

54

23°48.0'

109°40.5'

21.0

3.0

1

68

(continued)

144

Appendix: List of Stations (continued)

Stat.
No.

Date

Time f 7
from to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sed.
type

Device

47

29/

3/59

0750 0810

64

24 09.5'

109°48.0'

21.0

3.0

12

68

48

3ly

3/59

2300

2

24M1.5'

110°22.6'

23.0

4.0

79

50

1

4/59

0710 0715

92

119

25°26.0'

109°24.0'

10.0

2.0

72

68

51

1

4/59

1900

17

25°31.5'

109°13.5'

24.0

3.0

1

77

52

2

4/59

0110 0230

2141

2251

25'22.0'

110°00.0'

2.0

1.0

72

74

53

2

4/59

1034

920

272

25°31.8'

109°22.8'

12.0

2.0

71

78

54

2

4/59

1205

165

137

25°29.3'

109°24.3'

9.0

2.0

72

68

55

4l

4/59

0115 0125

37

27°45.0'

112°38.5'

18.0

3.0

1

68

56

4

4/59

0125 0135

69

27°45.0'

112°38.5'

15.0

3.0

1

68

57

4

4/59

0135 0145

64

27=45.0'

112°38.5'

18.0

3.0

1

68

58

5

4/59

1240

460

28=37.2'

113°02.5'

13.0

1.4

10

63

59

6

4/59

0904 1014

595

515

28"39.7'

113°02.5'

13.0

1.3

10

63

60

6

4/59

1200

1182

28^55.2'

11 3° 12.4'

12.0

1.6

2

51

61

7

4/59

1340

662

405

29°04.7'

113°20.1'

12.0

.9

78

62

8

4/59

1245 1330

532

625

29° 18.0'

113°39.9'

12.0

1.0

1

63

63

8

4/59

1605 1800

549

29"25.4'

113°45.0'

14.0

1.0

1

78

64

8

4/59

1025

92

29°30.5'

113°27.0'

19.0

3.0

1

71

65

9

4/59

0145

320

29°28.0'

113°02.0'

12.0

1.9

4

74

66

9

4/59

0730

420

28'53.8'

112°54.8'

11.0

1.1

1

53

67

9

4/59

1900

396

29°06.r

112°57.5'

11.0

1.5

1

53

68

9

4/59

2255

119

29°24.3'

113°19.0'

19.0

1.9

1

68

69

9

4/59

2340

119

29°34.3'

11 3° 19.0'

19.0

1.9

1

77

70

10

4/59

0110 0125

229

110

29°24.3'

113° 19.0'

19.0

1.9

1

68

71

10

4/59

0200 0215

73

29°20.0'

1 13°00.2'

13.0

2.3

12

68

72

10

4/59

0320 0335

132

29°24.6'

11 3° 19.0'

12.0

2.3

12

68

73

10

4/59

0745

397

29°04.5'

112°54.2'

11.0

1.2

1

53

74

10

4/59

0900

269

29° 10.8'

112°48.3'

11.0

2.3

1

53

75

10

4/59

1205

232

29° 19.0'

112°51.8'

12.0

2.4

5

53

80

18

4/59

0712 1700

430

30°01.0'

113°31.0'

11.0

1.9

1

63

81

25

4/59

1430 1525

1433

28°40.1'

113°01.9'

11.0

1.4

6

51

82

28

4/59

0807 2015

109

111

30°32.0'

113°26.0'

14.0

2.0

75

63

83

28

4/59

1330 1500

130

29°21.0'

112°42.0'

16.0

2.4

1

63

84

9

1 5/59

2145 0400

1410

1420

22°47.5'

106°52.0'

4.0

.5

70

74

85

9

5/59

1121 1245

435

22°44.0'

106°33.5'

4.0

.5

72

74

86

9

1 5/59

2100 2225

2030

22°38.5'

107°08.0'

2.0

1.0

72

77

87

10

5/59

1545 1635

57

44

23°56.6'

107°21.8'

24.0

3.0

72

72

88

10

5/59

1839 1935

77

88

23°50.5'

107°22.6'

24.0

3.0

72

72

89

11

5/59

0015 0115

109

128

23°47.3'

107°26.0'

12.0

1.5

70

72

90

11

5/59

0742 1240

1370

1382

23°38.9'

107°55.8'

4.0

.5

72

72

91

11

/ 5/59

1600 1715

724

738

23°54.7'

108°09.5'

5.0

.5

72

72

92

12

5/59

0900 0915

88

24°06.2'

107°49.1'

14.0

3.0

71

68

93

12

5/59

1030 1500

95

24°05.0'

107°49.2'

13.0

3.0

71

63

94

13

5/59

0040 0200

40

44

23°33.5'

106°50.7'

24.0

3.0

71

72

95

13

1 5/59

0220 0300

44

48

23°35.2'

106°53.5'

26.0

3.0

71

72

96

15

1 5/59

0015 0635

3001

2988

22° 11.2'

107°46.1'

2.0

2.0

72

72

97

18

/ 5/59

1910 2010

55

21°50.0'

106°09.4'

26.0

3.0

72

72

98

18

/ 5/59

2240 2340

37

47

21°48.0'

105°51.0'

14.0

3.0

72

72

100

31

/ 9/58

0900 1600

0

31°05.0'

114°45.0'

24.0

4.9

1

76

101

23

/ 3/59

0900 1600

0

22°45.0'

109°40.0'

30.0

5.0

10

76

102

26

1 3/59

0900 1600

2

22°45.0'

109°40.0'

30.0

5.0

1

76

103

28

1 3/59

0900 1600

0

23°33.0'

109°23.0'

30.0

3.0

10

76

104

29

/ 3/59

0900 1600

0

9

24° 10.0'

109°50.0'

25.0

3.0

10

66 76

105

1

/ 4/59

0900 1600

0

25°25.0'

109°25.0'

28.0

3.0

10

76

(continued)

145

Appendix: List of Stations (continued)

Stat.
No.

Date

Time + 7
from to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sad.
type

Device

106

5/ 4/59

1200

0

28''32.0'

112°45.0'

21.0

3.0

1

76

107

5/ 4/59

1200

0

28°32.0'

112°45.0'

21.0

3.0

10

76

108

5/ 4/59

1400

3

28°32.0'

112°45.0'

11.0

3.0

10

66

109

7/ 4/59

0900 1030

0

28°55.0'

113°31.0'

21.0

3.0

77

76

110

9/ 4/59

2300

0

29''20.0'

11 3° 15.0'

19.0

1.9

1

79

111

5/ 5/59

1500

5

23° 10.7'

106°25.8'

14.0

4.0

1

57

112

5/ 5/59

1630

2

23° 12.2'

106°25.6'

30.0

3.0

1

75

113

5/ 5/59

1100

7

23° 11.2'

106°25.9'

30.0

4.0

1

57

114

5/ 5/59

1730 1745

7

23°11.1'

106°26.0'

30.0

4.0

1

57

115

6/ 5/59

0900 1600

0

23° 13.9'

106°28.9'

24.0

3.0

77

76

116

6/ 5/59

0900 1600

0

23° 14.0'

106°28.2'

24.0

3.0

1

76

117

7/ 5/59

1600

0

23° 15.0'

106°28.8'

30.0

4.0

1

76

118

17/ 5/59

0630 1730

0

5

21°14.0'

106°20.0'

30.0

4.0

14

75 57

119

20/ 5/59

1430 1630

3

20°35.0'

105° 15.0'

30.0

4.0

14

66

125

17/11/58

0420 0450

238

15°45.0'

95°40.5'

14.0

.1

72

74

126

18/11/58

0855 1130

220

238

15° 17.5'

95°53.5'

14.0

.1

72

74

127

18/11/58

2056 0343

1006

1135

15°38.0'

95° 18.5'

8.0

.1

72

74

128

18/11/58

1500 1625

3529

3557

14^28.0'

95°09.0'

1.5

2.0

72

74

129

20/11/58

1510 1610

320

305

14°31.0'

93°09.2'

11.0

.1

72

74

130

20/11/58

1330 1520

403

14°24.0'

93°03.0'

10.0

.1

72

74

131

21/11/58

1520 1920

3596 3642

12°20.0'

91°51.0'

1.5

2.0

72

74

132

27/ 1/59

1200

20

22

32°35.0'

117°11.1'

10.0

3.0

1

74

133

27/ 1/59

1400 1500

92

32°31.9'

11 7° 17.5'

9.0

2.0

3

74

134

28/ 1/59

1405 1700

2013

32°39.2'

118°09.0'

2.5

1.3

10

74

135

29/ 1/59

0515 0650

1190

32°36.6'

117°35.2'

6.0

1.8

72

74

136

12/ 2/60

1940 2130

183

458

31°38.3'

116°51.4'

10.0

.5

10

63

137

13/ 2/60

1530 1700

2068

2086

31°16.4'

117°34.2'

2.5

1.3

81

71

138

15/ 2/60

2245 0100

875

1281

30° 11.9'

117°37.7'

4.0

.9

5

63

139

15/ 2/60

1702 2315

2708

2763

29°40.2'

117°06.6'

2.0

2.0

8

71

140

16/ 2/60

0638 0815

549

732

29°30.8'

117° 16.8'

8.0

.3

10

63

141

17/ 2/60

0926 1700

3009

3989

29°03.5'

116°41.5'

1.5

1.8

72

71

142

18/ 2/60

0430

567

29°37.0'

116°31.0'

8.0

.3

10

63

144

10/ 3/60

0050 0415

915

1858

33°36.3'

1 19°26.8'

2.5

1.0

72

70

145

11/ 3/60

0050 0510

1880

1936

33°40.5'

1 19°29.3'

2.5

1.0

72

70

146

11/ 3/60

0720 0800

1918

915

33°39.9'

119°28.2'

2.4

1.5

72

67

147

15/ 3/60

2100 2200

92

84

23° 10.9'

106°35.5'

14.0

2.0

72

69

148

16/ 3/60

0945 1035

18

24°09.4'

107°25.1'

30.0

3.0

1

69

149

17/ 3/60

1100 1200

11

24° 13.0'

107°26.5'

30.0

3.0

75

69

150

16/ 3/60

2015 2100

33

36

24°32.6'

108°03.0'

18.0

2.0

71

69

151

16/ 3/60

2215 2230

430

455

24°39.5'

108°01.0'

18.0

1.0

71

79

152

11/ 3/60

1026

116

22°06.7'

106° 17.2'

9.0

.9

12

78

153

17/ 3/60

0200

40

24°56.0'

108°33.5'

24.0

3.0

71

78

154

17/ 3/60

0515

40

25°04.0'

108°47.5'

11.0

1.5

71

78

155

17/ 3/60

0636

33

25°07.5'

108°54.5'

11.0

2.0

72

78

156

8/ 3/60

2200 0200

236

403

21°35.0'

106°06.6'

13.0

1.0

70

69

157

9/ 3/60

2115 0100

13

22

21°46.4'

105°45.2'

30.0

3.0

13

69

158

10/ 3/60

2245 0200

53

61

22°09.0'

106°08.0'

20.0

3.0

12

69

159

11/ 3/60

2200 0220

46

57

22°30.8'

106°01.2'

20.0

3.0

1

69

160

20/ 3/60

0900 1600

0

2r55.0'

106°37.0'

24.0

3.0

1

76

161

17/ 3/60

1125

55

25°24.5'

109° 18. 5'

11.0

2.0

72

63

162

20/ 3/60

1200

2

28°23.8'

1 1 1°29.8'

20.0

4.0

1

76

163

20/ 3/60

1730

0

28°26.8'

111°38.7'

20.0

4.0

1

76

164

21/ 3/60

0100 0200

75

64

28° 13.8'

1 1 1°46.7'

14.0

2.0

2

69

(continued)

10 V'idensk. Medd. fra Dansk naturh. Foren. Bd. 126.

146

Appendix: List of Stations (continued)

Stat.
No.

Date

Time + 7
from to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sed.
type

Device

21/ 3/60

1030

7

9

28°22.0'

111°31.5'

20.0

3.0

1

63

21/ 3/60

1415

84

28" 11.5'

1 1 1°40.0'

14.0

3.0

1

63

21/ 3/60

1920

1930

320

310

28°02.0'

1 1 1°47.2'

11.0

.5

1

69

22/ 3/60

1000

201

28° 10.8'

1 1 1°49.0'

II.O

1.0

1

68

22/ 3/60

1038

84

28° 12.6'

111°47.3'

14.0

1.0

1

68

22/ 3/60

1515

61

28° 16.0'

IH°44.8'

14.0

3.0

12

68

22/ 3/60

1600

42

28° 19.3'

111°42.3'

14.0

3.0

12

68

22/ 3/60

1730

13

28°23.3'

111°39.8'

20.0

3.0

12

68

22/ 3/60

2000

7

9

28°25.3'

1 1 1°39.0'

20.0

3.0

1

79

23/ 3/60

1535

61

28° 11.3'

1 1 1°37.0'

14.0

3.0

1

68

23/ 3/60

2040

26

28°31.0'

112°04.2'

13.0

1.2

2

68

23/ 3/60

2155

82

28°27.8'

112°08.8'

13.0

1.2

1

68

24/ 3/60

0130 0145

68

70

28°25.5'

112°06.r

13.0

1.2

1

63

24/ 3/60

0300

22

28°26.8'

112°00.9'

18.0

3.0

2

63

24/ 3/60

0900

1245

0

28°41.4'

1 1 1°55.0'

20.0

4.0

1

76

24/ 3/60

1430

9

28°40.5'

111°55.2'

20.0

3.0

1

76

24/ 3/60

1815

16

28°30.0'

1 1 r59.5'

18.0

3.0

1

68

24/ 3/60

1830

1900

18

28°30.0'

lir59.5'

15.0

2.5

1

69

24/ 3/60

2240

18

28°30.8'

111°53.6'

15.0

3.0

1

68

25/ 3/60

0005

15

28°26.0'

1 1 r55.4'

18.0

3.0

12

68

25/ 3/60

0100

57

28°20.9'

1 1 1°58.0'

13.0

2.4

1

68

25/ 3/60

0140

60

66

28° 17.5'

112°00.r

13.0

2.4

1

68

25/ 3/60

0230 0310

292

320

28° 12.9'

112°03.2'

11.0

.3

1

68

25/ 3/60

0755

42

28° 10.0'

1 1 r55.2'

13.0

3.4

2

68

25/ 3/60

0925

28

28°20.5'

1 1 1°50.0'

14.0

3.0

1

58

25/ 3/60

1010

13

28°24.6'

1 1 1°48.0'

18.0

3.0

1

68

25/ 3/60

2100 2200

35

26

28°41.0'

112°06.0'

15.0

3.0

4

69

24/ 3/60

2300

15

28°49.5'

112°00.1'

18.0

3.0

1

76

26/ 3/60

2200

6

28°51.3'

1 1 1°58.0'

20.0

3.0

1

79

27/ 3/60

0822

13

28°54.9'

112°14.0'

20.0

3.0

2

68

27/ 3/60

0915

22

28°50.5'

112°11.0'

18.0

3.0

2

68

27/ 3/60

1100

24

28°45.8'

112°04.0'

16.0

3.0

1

68

27/ 3/60

1145

24

28°43.8'

112°09.1'

16.0

3.0

77

63

27/ 3/60

1335

92

28°41.6'

112°11.0'

14.0

1.5

12

68

27/ 3/60

1450

278

28°39.2'

112°26.4'

12.0

1.6

6

63

27/ 3/60

1555

298

28°39.5'

11 2' 29.0'

11.0

1.6

78

63

27/ 3/60

1700

230

28°30.0'

112°22.0'

11.0

1.2

1

68

27/ 3/60

1800

187

28°31.1'

11 2° 17.9'

11.0

2.0

4

68

27/ 3/60

1840

128

119

28°30.0'

112°16.2'

11.0

1.4

63

27/ 3/60

2010

77

28°36.6'

112°05.0'

14.0

1.3

63

28/ 3/60

0930

6

28°41.4'

1 1 1°55.9'

18.0

3.0

76

29/ 3/60

0930

1645

0

28°56.0'

112°14.r

20.0

4.0

76

29/ 3/60

1950

7

29° 16.5'

112°24.1'

18.0

3.0

79

30/ 3/60

1345

13

29°53.8'

112°45.5'

19.0

2.6

68

30/ 3/60

1515

73

29°51.8'

112°46.8'

14.0

2.6

68

30/ 3/60

1550

73

77

29°50.9'

112°49.0'

15.0

2.6

68

30/ 3/60

1945 2045

110

108

29°54.3'

113°03.2'

15.0

2.0

69

31/ 3/60

2340 0040

67

57

30°20.5'

113°20.5'

14.0

1.9

75

69

9/ 4/60

1913

2055

366

238

28°57.0'

113°22.0'

12.0

2.0

5

63

29/ 5/60

0905

1089

32°44.5'

117°43.0'

4

77

29/ 5/60

1026

1080

32°44.0'

117°43.0'

4

63

29/ 5/60

1700

1107

32°51.5'

11 7° 16.3'

2

77

30/ 5/60

0803

115

32°51.7'

11 7° 16.2'

2

77
continued)

147

Appendix: List of Stations (continued)

Stat.
No.

Date

Time +7
from to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sed.
type

Device

218

30/ 5/60

0836

231

32°51.2'

11 7° 16.3'

75

77

219

30/ 5/60

0924

318

32°52.2'

117°16.7'

1

77

220

30/ 5/60

1030

415

32°53.4'

117°18.7'

4

77

221

30/ 5/60

1600

1043

32°45.7'

117°38.7'

79

77

2'>2

8/ 3/60

31

32°33.4'

11 7° 13. 2'

2

74

22,1

9/ 3/60

220

31°04.5'

116°29.5'

72

74

224

30/ 5/60

1328

628

32^54.8'

117°24.7'

2

77

2.^5

6/11/60

1815 2215

1903

33°38.0'

1 19°28.0'

72

70

256

9/11/60

0500 0745

1669

2198

34°56.0'

121°49.5'

72

70

257

11/11/60

0415 0720

1830

37°35.7'

123° 15.2'

72

70

25S

30/ 3/60

0445 0525

906

37°34.0'

123° 16.0'

72

70

259

31/ 3/60

0350 0715

2028

37°34.5'

123°16.7'

72

70

2(30

1/ 4/60

0435 0815

1980

37°34.3'

123° 18.8'

72

70

261

30/11/60

2100 2220

106

26^01.7'

112°57.5'

13.0

.1

72

70

262

1/12/60

0045 0135

103

25°52.3'

112°49.2'

12.9

.2

1

80

263

2/12/60

0227 0403

42

26°24.8'

113°00.5'

17.0

3.0

4

69

264

2/12/60

1230 1350

183

292

26°04.5'

113°34.0'

11.0

1

69 80

265

3/12/60

292

28°36.0'

115°34.5'

11.0

72

69

266

3/12/60

2045 2135

101

29°07.8'

115°23.2'

13.0

.1

7

69

267

4/12/60

0753 0840

118

30^17.2'

116°03.2'

10.2

.1

72

69

268

2/12/60

0840 0915

92

82

26° 12.5'

11 3° 18.2'

13.3

2.1

72

80

269

30/ 5/60

1200

42

32°51.5'

11 7° 16.0'

1

77

270

9/ 3/59

1816

9

24°51.7'

108°14.3'

24.0

4.0

1

59

271

10/11/60

1800 2300

2380

37°36.5'

123° 18.5'

72

70

272

7/11/60

0100 0530

1907

33°36.4'

119°30.0'

72

70

273

9/11/60

0130 0445

1630

34°46.0'

121°46.6'

72

70

274

28/ 4/61

2205 0245

1986

1975

30°52.0'

116°53.0'

2.5

1.3

4

71

275

29/ 4/61

0835 1345

2782

2779

29°59.5'

116°33.2'

2.0

2.0

72

71

276

29/ 4/61

2200 0550

4062 4050

28°57.8'

116°39.0'

1.5

2.0

72

71

277

1/ 5/61

1040 1720

3547 3450

24°45.0'

113°27.0'

1.6

2.0

72

73

278

2/ 5/61

0420 0530

40

43

25°57.7'

11 2° 19.8'

13.0

1.1

72

80 70

279

2/ 5/61

0725 0805

73

80

25°54.3'

112°32.0'

12.0

.6

72

70

280

2/ 5/61

1000 1050

121

116

25°43.0'

112°51.4'

12.0

.6

72

70

281

2/ 5/61

1215 0200

147

163

25°42.8'

112°55.0'

11.0

.5

72

70

282

2/ 5/61

1410 1500

190

218

25°43.0'

112°59.9'

10.0

.4

72

70

283

2/ 5/61

1510 1550

201

164

25°43.0'

113°02.5'

10.0

.4

72

70

284

2/ 5/61

1700 1938

274

293

25°30.0'

112°56.6'

10.0

.4

72

70

285

3/ 5/61

0845 1530

3481

3518

23°59.5'

113° 11.9'

2.5

2.8

72

73

287

6/ 5/61

1635 0040

4191

4163

27°20.0'

115°23.1'

1.2

2.9

72

73

288

12/ 3/60

1211

11

22°41.0'

105°53.8'

30.0

3.0

73

59

289

12/ 3/60

1250

17

22°39.7'

105°56.7'

30.0

3.0

12

59

290

3/ 3/59

0020

168

23°23.5'

106°45.5'

72

53

291

4/ 2/59

2227

888

28°29.4'

112°44.3'

72

53

292

16/ 1/58

1200 1600

24

16°38.0'

99°58.0'

30.0

2.0

4

66

293

21/ 6/59

1100 2200

1190

32°35.5'

1 17°28.5'

6.0

1.8

72

81

296 A

18/ 3/59

1020

11

26°I6.5'

112°38.2'

22.0

5.0

1

59 57

297 A

24/ 3/59

0900 1600

18

22°45.0'

109°40.0'

30.0

5.0

10

66

296 B

11/62

18

22°54.8'

106°08.0'

297 B

11/62

62

22°21.2'

106°08.5'

298

11/62

57

22°22.0'

106°05.3'

299

11/62

53

22°23.2'

106°02.0'

300

11/62

48

22°24.4'

105°59.0'

301

11/62

22°26.5'

105°52.2'

10=>

(continued)

148

Appendix: List of Stations

Stat.
No.

Date

Time + 7
from to

Depth m.
from to

Latitude

Longitude

Temp.
°C.

Oxyg.

ml/L

Sed.
type

Device

302

11/62

303

11/62

304

11/62

305

11/62

306

11/62

307

11/62

308

11/62

309

11/62

310

11/62

311

11/62

312

11/62

313

11/62

314

11/62

22

22°27.7'

105''49.0

13

22° 12.0'

105°42.5

68

22°01.0'

106° 14.3

71

21°52.0'

106°11.8

53

21°53.0'

106°09.8

62

21°43.4'

106° 12.8

71

21°42.0'

1 06° 15.5

115

21°41.0'

106° 17.5

104

21°40.6'

106° 15.0

78

21°43.0'

106° 16.0

90

21°43.4'

106° 16.4

59

21°12.5'

105°25.5

83

21°04.3'

105°27.5

Key to Code Numbers used under Sediment Type and Device Headings
in Station Data Table

Sediment Type Code

Sample Device Code

Code

Number

Sediment Type

Code

Numbei

Device

1

sand

51

Gravity Core

2

muddy sand

52

PBS Core

3

sandy mud

53

Piston Core

4

mud

57

Van Veen Grab

5

gravel

58

Snapper Grab

6

gravel and sand

59

Orange Peel Grab

8

hard clay

63

Rock or Chain Dredge

10

rock

66

Diving

11

shell

67

Plankton Net

12

shelly sand

68

Shell Dredge

13

shelly mud

69

10' Otter Trawl

14

coral

70

16' Otter Trawl

70

clay

71

30' Otter Trawl

71

clayey silt

72

40' Otter Trawl

72

silty clay

73

10' Beam Trawl

73

sand-silt-clay

74

Deep Diving Dredge

74

clayey sand

75

Mini-dredge

75

silty sand

76

Hand Collecting

77

sand and rock

77

1/10 m2 and 1/5 m^ Petersen Grab

78

shell-mud-sand

78

Box or Pipe Dredge

79

sandy silt

79

Dipnet

81

silty clay and rock

80

Closing Dredge

81

Isaak's Fish Trap

82

Mid-water Trawl

149

Explanation of Table I

1. Under list of species: Series of numbers preceeding every species name is the IBM code
number for that species, and identifies that species on the IBM species-data cards. These
numbers can be referred to for any future programs which might be carried out utilizing
the data in this study.

2. The systematic arrangement of species in this list follows a number of authorities including
Keen (1958), Mortensen's "Monograph of the Echinoidea", John Garth's various papers
on Decapod Crustacea of the eastern Pacific, Hyman's volumes on the invertebrates:
Protozoa through Echinoderms, and various other monographic series. Specialists may not
always agree completely as to the systematic arrangement, but an attempt was made to
consult with leading specialists in each group of invertebrates.

3. Species names are not italicized, as the list of names were printed-out by an IBM machine
which has only one kind of type.

4. The station numbers which are underlined are those stations at which living animals were
found for that species.

5. Depth ranges are given in fathoms, since the original data had been plotted in fathoms, and
time did not permit a complete conversion to meters.

6. Living depth ranges are given by a solid line, while distribution of dead shell or tests is
given by dotted lines.

7. The code numbers (Roman numerals) under the Environment column correspond to the
numbers of the environments given throughout the text.

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166

Appendix: Table II. Supplemental Lists of Invertebrate Species from
Various Gulf of California Environments^

1. Intertidal Rocky Shores:

Anthozoa
Pocillopora porosa

Amphineura
Acanthochitona angelica
Acanlhochitona exsquisita
Chiton articulatus
Chiton goodalii
Callistochiton gahhi
Lepidozona clathrata
Lepidozona subtilus

Prosobranchiata
Acmaea discors
Acmaea fascicularis
Acmaea mitella
Acmaea semirubida
Patella mexicana
Nomeopelta dalliana
Nomeopelta mesoleuca
Fissurella longifissa
Fissurella rugosa
Diodora alta
Tegula globulus
Tegula ligulata
Turbo fluctuosus
Nerita scabricosta
Nerita funiculata
Liltorina aspersa
Littorina conspersa
Littorina dubiosa pencillata
Littorina pullata
Vermicularia pcllucida
Petalochonchus macrophyllum
Cerithium sculptum
Cerith ium stercusmuscarum
Thais biserialis

Li\'ing only.

Acanthina lugubris
Acanthina tuberculata
Morula fcrruginosa
Purpura patula pansa
Pyrene fuscata
Cantharus macrospira
Marginella californica
Crassispira nympha
Conus purpurescens

Pulmonata
Siphonaria maura maura
Onchidiella binneyi

Lamellibranchiata
Barbatia illota
Barbatia reeveana
Arcopsis solida
Brachidontes multiformis
Isognomon chemnitzianus
Cardita affinus californicus

Crustacea
Grapsus grapsus

Holothuroidea

Brandtothuria impatians
Athyone glanelli

Asteroidea*
Greasier occidentalis Verrill
Linckia Columbia (Gray)

Echinoidea
Diadema mexicanum

Prosobranchiata
Fissurella virescens
Diodora saturnalis
Turbo squamiger
Neritina luteofasciata
Petaloconchus conlortus
Hipponix antiquatus
Cypraea annettae
Trivia californiana
Jenneria pustulata
Cymatium gibbosum

Abundant, but not living at time of collection.

Pyrene strombiformis
Nassarius tiarula

Lamellibranchiata
Area pacifica
Barbatia alternata
Ostrea conchaphila
Anomia adamas
Anomia peruviana
Pseudochama inermis

>) This list contains all living, identified species from all significant stations for environments,
whenever these lists are not in the main body of the text.
* Added after Table I was prepared.

167

II. Intertidal Sand Beaches and

Prosobranchiata
Cerithium maciilosum
Cerithidea albonodosa
Strombus gracilior
Oliva spicata
Olivella anazora
Bulla gouldiana

Scaphopoda
Cadulus austinclarki

Lamellibranchiata

Cardita grayi

Cardita megastropha

Codakia distinguenda

Transanella puella

Pilar lupanaria

Megapitaria squalida

Anomalocardia subimbricaia lumens

Sand-Flats to 10 Meters:

Living only.

Tellina felix
Macoma pads
Heterodonax bimaculalus

Crustacea
Clibanarius digueli
Neopanope pelerseni
Ocypode occidentalis Stimpson^
Uca crenulala

Holothuroidea
Selenkothuria lubrica
Thyone parafusus
Neolhyone gibbosa

Echinoidea
Eucidaris Ihouarsi
Echinomelra vanbrunli
Brissus lalicarinalus

Prosobranchiata
Nerilina luleofasciala
Turrilella gonostoma
Turrilella leucosloma
Cerilhium uncinalum
Cypraea arabicula
Slrombus granulalus
Cassis coarclala
Nassarius angulicoslis
Nassarius tiarula

Lamellibranchiata

Anadara mullicoslata
Anadara labiosa
Glycymeris delesserlii
Alrina mama
Cardila grayi
Cardila lalicoslala
Cardila radiala
Diplodonla subquadrala
Diplodonta sericala
Trachycardium procerum

Abundant, but not living at time of collection.

Papyridea aspersa
Tivela byronensis
Pilar concinna
Megapilaria squalida
Dosinia dunkeri
Dosinia ponderosa
Chione californiensis
Chione compla
Chione picla

Anomalocardia subimbricaia
Prololhaca meladon
Prololhaca grala
Analina undulata
Mulinia pallida
Tellina erythronotus
Donax assimilis
Donax californicus
Donax carinatus
Donax punctostriatus
Tagelus affinus
Semele guaymasensis
Pholas chiloensis

IV. Nearshore Shelf, Sand Bottom, 11 to 26 Meters, Northern Gulf:

Living only.
Hexacorallia Prosobranchiata

Heterocyathus aequicostatus

Aslrangia corlezi
Aslrangia pedersonii

Calliostoma bonila
Niso excolpa
Turrilella leucosloma

1) Seen on beaches, identified in Scripps Institution collections from Gulf of California,
but not collected as part of this study.

168

Prosob ranchiata (continued)
Architedonica nobilis
Calyptraea conica
Calyptraea mamillaris
Calyptraea siibreflexa
Crepidula arenata
Crepidula excavata
Crepidula incurva
Crepidula perfnrans
Crucibulum scuttelalum
Crucibulum serratum
Crucibulum spiriosum
Polinices reclusiamis
Sirornbus gracilior
Hexaplex erythrostomus
Eupleura muriciformis
Anachis adelinae
Anachis varia
Strombina solidula
Cantharus pallidus
Phos articulatus
Nassarius pagodus
Nassarius versicolor
Fusinus ambustus
Oliva incrassata
Oliva spicata pol pasta
Olivella dama
Olivella fletcherae
Olivella gracilis
Mitra hindsii
Lyria cummingii
Cancellaria balboae
Cancellaria cassidiformis
Cancellaria decussata
Cancellaria obesa
Claims roseolus
Clavus pembcrtonii
Clavus unimaculatus
Clathrodrillia pilsbryi
Crassispira nephele
Crassispira labogcnsis
Crassispira xanti
Hormospira maculosa
Pleuroliria picta
Conus perplexus
Conus scalaris
Terebra armillata
Terebra malonei
Terebra spccillata
Terebra tuberculosum
Terebra variegata
Pyramidella adamsi

Lamellibranchiata
Nuculana acrita
Nuculana costellata
Nuculana elenensis
Nuculana fastigata
Nuculana impar
Adrana exoptata
Adrana penascoensis
Adrana tonosiana
Anadara obesa
Lioberus salvadoricus
Pecten sericeus
Chlamys circularis
Crassatella gibbosa
Trachycardium panamense
Laevicardium datum
Laevicardium elenense
Pilar concinnus
Pilar newcombianus
Megapitaria aurantia
Megapitaria squalida
Chione compta
Chione mariae
Cooperclla subdiaphana
Tellina amianta
Tellina arenica
Tellina iris
Tellina tabogensis
Macoma siliqua
Donax gracilis
Ensis californicus
Corbula luteola
Corbula nasuta
Corbula ovulata
Pandora claviculata
Lyonsia gouldii

Crustacea
Balanus trigonus
Balanus concavus mexicanus
Munida tendla
Euceramus transverslineatus
Minyocerus kirki
Porcellana cancrisoc talis
Dardanus sinistripes
Paguristes digueti
Paguristes praedalor
Pagurus bcnedidi
Pagurus gladius
Petrochirus californiensis
Pylopagurus varians
Parapylochdes glasselli

Scaphopoda
Dentalium oerstedii
Dentalium inversum
Cadulus perpusillus

Echinoidea
Arbacia incisa
Encope micropora
Clypeastcr, sp.

169

Echinoidea (continued)
Mellita, sp.
Lovenia cordiformis
Brissopsis pacifica
Moira clot ho

Ophiuroidea*
Amphiodia occidentalis (Lyman)

IV. Nearshore Shelf, Sand Bottom, 11 to 26 Meters, Southern Gulf:

Hexacoraliia
Astrangia conferta^

Prosobranchiata
Architectonica placental is^
Calyptraea mamillaris
Crepidula aculeata
Crepidula incurva
Natica broderipiana
Natica chemnitzii^
Natica othello^
Polinices intemerata
Polinices uber
Sinum debile''-
Sinum sanctijohannis^
Ficus ventricosa
Distorsio decussatiis^
Bursa nana
Eupleura muriciformis
Typhis cummingii^
Strombina hirundo
Cominella subrostrata^
Cantharus capitaneous
Nassarius pagodus
Oliva incrassata
Olivella anazora^
Olivella flelcherae
Mitra hindsii
Cancellaria exopleiira^
Hormospira maculosa
Conus perplexus
Terebra armillata
Terebra variegata

Lamelli branch lata
Nucula declivis
Nuculana elenensis
Anadara concinna
Anadara nux^
Anadara, sp.
Atrina maura
Chlamys circularis
Chlamys tumbezensis^

Lucina cancellaris
Ctena clarionensis
Trachycardium pananiense
Transanella puella
Pilar concinnus
Pilar frizzeli^
Megapitaria squalida
Dosinia dunkeri
Chione gnidia
Chione, sp.
Mulinia bradleyi^
Tellina cognata^
Tellina felix
Macoma, sp.
Tagelus politus
Corbula nasuta
Corbula ovulata
Pandora claviculata
A bra palmeri^
Lyonsia gouldii
Periploma, sp.

Crustacea
Balanus trigonus
Euceramus panatelus^
Dardanus sinislripes
Pagurisles praedator
Pagurus gladius
Pagurus smithi^

Echinoidea
Moira clotho
Brisaster toivnsendi (A. Agassiz)

Asteroidea*
Astropecten californicus Fisher (juv.)

Ophiuroidea
? Amphiura seminuda Liitken and
Mortensen.

1) These species confined primarily to the southern Gulf.
* Added after completion of Table 1.

170

V. Intermediate Shelf, Sand Bottom, 27 to 65 Meters, Northern Gulf:

Living only.

Hexacorallia
Hetcrocyathiis aequ icostatus

Prosobranchiata
Calliostoma nepheloide
Solariella triplostephanus
Calyptraea mamillaris
Crepidulz excavata
Crepidiila striolata
Crucibulum concameratum
Crucibuhim scultelatum
Natica grayi
Cassis centriquadratum
Ficus ventricosus
Murex recurvirostris
Strombina gibberula
Nassarius pagodus
Nassarius versicolor
Fusinus colpoicus
Fusiniis diipetitthouarsi
Olivella fletcherae
Mitra sulcata
Lyria cummingii
Knefastia luberculifera
Clavus melea
Claims pallidas
Crassispira ericana
Hindsiclava dotella
Turricula armilda
Pleuroliria albicarinata

Lamellibranchiata
Anadara cepoides
Anadara mix
Anadara obcsa
Liobenis Salvador icus
Chlamys circularis
Crassatella gibbosa
Trigoniocardia biangulata
Laevicardium elatum
Nemocardium pazianurn
Transanella puella
Pilar newcombianus
Chione mariae
Tellina inaequistriata
Macoma medioamericana
Macoma siliqua
Macoma undulata
Pandora granulata
Plecladon scaber

Crustacea
Balanus concajus mexicanus
Balanus trigonus

Munida lenella
Pleuroncodes planipes
Porcellana cancrisocialis
Dardanus sinistripes
Paguristes bakeri
Paguristes praedator
Pagurus benedict i
Pagurus californicus
Pagurus gladius
Pagurus smithi
Pylopagurus varians
Hypoconcha loivei
Calappa sausserei
Hepatus lineatus
Randallia americana
Randallia ornata
Lithadia cummingii
Cancer amphioetus
Portunus iridescens
Portunus minimus
Portunus pichilinquei
Micropanope polita
Mesorhea belli
Collodes tenuirostris
Euprognatha bifida
Paradasygius depressus
Podochela hemphilli
Pyromaia tuberculata
Stenocionops ovata
Cymopolia fragilis
Cymopolia zonula
Clythrocerus laminatus
Ethusa lata

Pseudorhombila xanthiformis
Pinnotheres, sp.

Echinoidea
Arbacia incisa
Clypeaster europacificus
Clypeaster, sp.
Lovenia cordiformis
Agassizia scrobiculata
Brissopsis pacifica
Meoma grandis

Asteroidea*
Luidia Columbia Liitken
Astropecten californicus Fisher (juv.

Ophiuroidea
Amphigyptis perplexa Niels n

Added after compl tion of Table I.

171

V. Intermediate Shelf, Sand Bottom, 27 to 65 Meters, Southern Gulf:

Hexacorallia
Heterocyathus aequicostatus^

Frosobranchiata
Calliostoma bonita
Astele rerna

Architectonica placentalis
Calyptraea conica
Crucibulum scuttelatum^
Crucibulum spinosum
Natica broderipiana
Natica colirna
Natica grayi
Polinices otis
Polinices uber
Sinum pazianum
Distorsio decussatus
Bursa caelata
Bursa nana
Murex elenensis
Murex recurvirostris
Hexaplex brass ica
Ocenebra perita
Ocenebra cf. vitatla
Eupleura muriciformis
Coralliophila hindsii
Cosmioconcha cf. palmer i
Strombina marksi
Cantharus capitaneus
Phos articulatus
Hindsia acapulcana
Nassarius pagodus
Nassarius versicolor
Latirus hemphilli
Fusinus centrifugus
Fusinus colpoicus^
Fusinus dupetitthouarsi^
Mitra erythrogramma
Milra hindsii
Gemmula hindsiana
Knefastia walkeri
Clavus roseolas
Clavus walkeri
Clathrodrillia alcestris
Hindsiclava andromeda
Turricula fusinella
Pleuroliria albicarinata^
Pleuroliria picta
Terebra specillata

Scaphopoda
Dentalium oerstedii oerstedii^
Dentalium oerstedii numerosum

Living only, sand bottom.

Lamellibranchiata
Nuculana eburnea
Nuculana morella
Glycymeris multicostata
Glycymeris tessellata
Atrina, sp.
Chlamys circularise
Plicatula inezana
Cardita spurca beebei
Trachycardium belcheri
Lophocardium cummingii
Nemocardium pazianum^
Chione mariae
Tellina pristophora
Semele paziana

Crustacea

Balanus concavus mexicanus^
Porcellana cancrisocialis^
Clibinarius, sp. indet.
Dardanus sinistripes^
Paguristes digueti
Paguristes praedator^
Pagurus gladius^
Pylopagurus varians^
Parapylocheles glasselli
Hypoconcha lowei^
Calappa sausserei^
Hepatus kossmanni
Iliacantha hancocki
Persephona townsendi
Randallia bulligera
Lithadia cumingii^
Portunus acuminatus
Portunus affinus
Euphylax robustus
Medaeus lobipes
Leilolambrius punctatissimus
Heterocrypia macrobrachia
Solenolambrus arcuatus
Collodes gibbosus
Collodes tenuirostris^
Euprognatha bifida^
Paradasygius depressus^
Pyromaia tuberculata^
Stenorhynchus debilis
Notolopus lamellatus
Ethusa lata

Ethusa mascrone americana
Oediplax granulata
Chasmophora macropthalma
Prionoplax cf. ciliata

1) Indicates the same species found within the same depth range in the northern Gulf also.

172

V. Intermediate Shelf, Clay bottom, 27 to 65 Meters, Southern Gulf:

Living only, clay bottom.

Prosobranchiata
Architectonica nobilis
Crcpidula arenata
Crepidula excavata^
Crucibulum lignarium
Crucihulum spinosum
Xenophora robusta
Natica broderipiana
Natica elenae
Polinkes uber
Distorsio constriclus
Distorsio decussatus
Bursa nana
Murex recurvirostris
Ocenebra, sp.
Cantharus capitaneus
Fusinus depetitthouarsi^
Harpa crenata
Hormospira maculata
Conus arcuatus
Conus perplexus
Conus recurvus
Conus scalaris

Scaphopoda
Dentaliuni oerstedii oerstedii^

Lamellibranchiata
Noetia delgada
Glycymeris tessellala
Chlamys circularise
Plicatula inezana
Plicatula penicillata
Anodontia edentuloides
Pseudochama saavedrai
Trachycardium belcheri
Pilar catharius
Megapitaria squalida

Chione kelletti
Chione mariae^
Semele paziana

Crustacea
Balanus concavus mexicanus^
Porcellana cancrisocialis^
Clibinarius panamensis
Dardanus sinislripes^
Paguristes praedalor^
Pagurus gladius^
Pagurus smithi^
Pelrochirus californiensis
Pylopagurus varians^
Hypoconcha lowei^
Calappa sausserei^
Cycloes bairdii
Hepalus kossmanni
lliacantha hancocki
Persephone lownsendi
Randallia bulligera
Porlunus acuminatus
Portunus affinus
Porlunus asper
Euphylax robuslus
Medaeus lobipes
Leilolambrus punclalissimus
Collodes gibbosus
Collodes tenuiroslris^
Collodes lumidus
Paradasygius depressus^
Pyromaia luberculala^
Stenorhynchus debelis
Elhusa lata
Oediplax granulatus

Holothuroidea
Thyonaeta mexicana

VI. Outer Shelf, Clay bottom,

Prosobranchiata
Archileclonica nobilis
Calyptraea conica
Crepidula excavata
Crepidula incun'a
Crucibulum serratum*
Crucibulum, n. sp.*
Distorsio constrictus
Distorsio decussatus
Ocenebra sloati, n. ssp.
Strombina clavulus
Strombina, n. sp.*

66 to 120 Meters, Southern Gulf:

Cantharus capitaneus
Cantharus, n. sp.*
Phos cococensis
Phos, n. sp.
Nassarius cattalus
Clathrodrillia, sp.
Hormospira maculosa
Pleuroliria oxytropis
Tiaturris spectabilis (dead ?)
Conus arcuatus*
Conus recurvus

') Indicates same species found within the same depth range in the northern Gulf too.
* Most abundant and characteristic living species.

173

Scaphopoda
Dentalium splendidum

Lamellibranchiata
Nuculana laeviradius
Anadara mazatlanica'^
Anadara concinna
Anadara emarginata*
Anodontia edentuloides*
Chione kelletti'*
Corbula luteola
Corbula obesa*
Periploma carpenteri*
Cuspidaria pedinata

Crustacea
Heterocarpus vicarius
Solenocarpus, sp.

Pleuroncodes planipes
Dardanus sinistripes
Calappa sausserei
Mursia guadichaudi
Cancer porteri
Portunus iridescens
Medaeus lobipes
Stenorhynchus debilis
Ethusa ciliafrons''

Polychaeta
Protula snperba''

Echinoidea
Spatangus californiciis*

Most abundant and charucterstic living species.

VII. Outer Shelf, Sand Bottom, 66 to 120 Meters, Northern Gulf:

Living only.

Hexacorallia Scaphopoda

Ceratotrochus franciscana Dentalium oerstedii

Astrangia, sp.

Opisthobranchiata
Cyclichna, sp.
Doridae
Eugorgia, sp. Rhizorus, sp.

Triopha, sp.

Octocorallia
ugorgia, sp.
Leptogorgia, sp.

Prosobranchiata

Calyplraea conica
Calyptraea mamillaris
Crepidula onyx
Crucibulum lignarium
Polinices intemerata*
Polinices otis
Sinum pazianum
Cymatium amictum*
Murex recurvirostris
Nassarius insculptus gordanus*
Fusinus dupetitthouarsi
Fusinus, sp.
Clavus cf. craneanus
Clathrodrillia, sp.
Hindsiclava andromeda
Mangelia, sp.
Turricula armilda*
Turricula nigricans
Pleuroliria artia*
Pleuroliria nobilis*
Pleuroliria oxytropis
Pleuroliria oxytropis albicarinata

* Abundant or characteristic species.

Lamellibranchiata
Nucula exigua*
Nuculana laeviradius
Amygdalum pallidulum
Plicatula inezana
Lucina excavata
Lucinoma annulata*
Nemocardium centrifilosum*
Nemocardium pazianum
Pilar catharius*
Chione mariae
Macoma medioamericana*
Corbula fragilis
Corbula luteola
Corbula obesa
Corbula ventricosa*
Pandora cf. brevifrons*
Cyathodonta dubiosa*

Crustacea

Munida tenella
Minyocerus kirki
Paguristes praedator

174

Crustacea (continued)
Pylopagurus holmesi
Pylopagurus longicarpus
Spiropagurus occidentalis
Hypoconcha lowei
Calappa sausserei
Iliacantha hancocki
Persephona townsendi
Randallia americana
Randallia angelica
Randallia ornata
Ebalia cristata
Cancer amphiodus
Lophopanopeus frontalis
Mesorhea belli
Heterocrypta macrobrachia
Collodes tenuirostris
Collodes tumidus
Euprognatha bifida
Paradasygius depressus
Podochela lobifrons
Pyromaia tuberculaia
Sphenocarcinus agassizi
Stenocionops beebei

* Added after Tall: I was prepared.

Stenocionops ovata
Slenorhynchus debilis
Inacoides laevis
Libinia mexicana
Cymopolia fragilis
Cymopolia zonata
Clythrocerus planus
Ethusa lata

Chasmocarcimis latipes
Speocarcinus granulimanus

Holothuroidea
Parastichopus californicus
Vaneyothuria zacae

Echinoidea
Hesperocidaris perplexa
Clypeaster europacificus
Encope grandis

Asteroidea*
Astropecten californicus Fisher (juv.)
Diopederma danianiim (Verrill)

VIII. Northern Gulf Basins and Troughs, 230 to 1,500 Meters:

Living and dead.

Octocorallia
Acanthagorgia, n. sp. live
Callogorgia flabellum live
Eumuricea horrida live

Hexacorallia
Ceratotrochus, sp.
Coenocyathus bowersi live
Desmophyllum crista-galli live
Desrnophyllum, sp.
Balanophylia, sp.
Astrangia, sp.
Dendrophyllia cortezi live
Dendrophyllia, sp.
Bathycyathiis, sp.
Porites, sp.

Brachiopoda
Morrisia hornei live
Terebratalia obsoleta^
Terebratulina cf. kiiensis live
Terebratulina, sp.
Argyrotheca loiveii^
Laqueus californicus live

Amphineura
Genus and species unidentified live

* Abundant or characteristic species.

1 Also taken on upper slope of southern Gulf.

Prosobranchiata
Acmaea, sp.

Emarginula velascoensis^
Rimula, n. sp. A.
Rimula, n. sp. B.
Fissurella, sp.
Diodora alta
Diodora aspera
Calliostoma gemnmlatum
Calliostoma variegatum
Calliostoma, n. sp.
Margarites albolineatus
Solariella cf. elegantula
Solariella permabilis
Solariella, sp.
Turcica caffea
Turbo, sp.
Liotia cookeana
Arene, sp.

Epitonium cf. manzanillense
Epitonium cf. obtusum
Circostrema cf. dalli (Atlantic sp.)
Caecum, sp.
Turritella cf. cooperi
Crepidula onyx
Crucibulum scuttelatum
Crucibulum, sp.
Torellea I'allonia

175

Prosobranchiata (continued)
Polinices intemeratus^
Polinices otis
Natica chemnitzii
Cypraea annettae
Ficus ventricosa
Cymatium adairense
Cymatium amictum
Pterynotis carpenteri
Strombina, sp.
Pyrene fuscata
Boreotrophon, n. sp.'
Metula amosi
Nassarius cattalus^
Nassarius insculptus gordamis^
Nassarius, sp.
Fusinus barbarensis
Fusinus colpoicus^
Fusinus traski live
Mitra crenata
Mitra marshalli
Antiplanes abarbarea
Hindsiclava cf. andromeda
Pleuroliria oxytropis
Cavolina longirostris

Scaphopoda
Dentalium oerstedii^
Dentalium pretiosum berryi live
Dentalium vallicolens^
Dentalium, n. sp.
Dentalium ( Laevidentalium) , sp.'
Cadulus perpusillus^
Cadulus austinclarki live
Siphonodentalium quadrifissatum 1

Opisthobranchiata

Cyclichna, sp.
Cyclichnella, sp.
Retusa, sp.
Sulcaretusa, sp.
Tornatina, sp.

Lamellibranchiata
Solemya valvulus^ live
Acila castrensis^ live
Nuculana taphria live
Nuculana hamata
Yoldia martyria
Area nucleator

Barbatia bailey i
Barbatia gradata
Barbatia alternata
Anadara cepoides
Glycymeris corteziana
Glycymeris lintea
Glycymeris maculata
Glycymeris multicostata^
Amygdalum pallidulum^ live
Pododesmus cepio
Pecten vogdesi^
Chlamys, n. sp.
Cyclopecten exquisitus
Cyclopecten pernomus
Cyclopecten vancouverensis
Cyclopecten zacae^
Dimya calif or nica
Crassinella varians
Cardita barbarensis^
Cardita megastropha
Lucina tenuisculptus^
Lucinoma annulata^ live
Diplodonta inezensis
Thyasira, sp.
Chama squamuligera
Pseudochama, sp.
Trigon iocardia guanocastensis
Nemocardium centifilosum^ live
Ventricolaria isocardia
Tellina bodegensis
Tellina carpenteri
Macoma planuiscula
Macoma siliqua spectri live
Semele quentinensis
Corbula martnorata
Corbula tenuis
Hiatella arctica
Verticordia aequicostata
Verticordia ornata

Crustacea
Salmoneus, sp.

Echinoidea
Hesperocidaris perplexa live
Spatangus, sp.
Brisaster townsendi live
Brissus, sp.

Asteroidea*
Astropecten ornatissimus Fisher

1) Also taken on upper slope of southern and central Gulf. Unless indicated species were
taken as dead Shell.

* Added after Table I was prepared.

176

St. Number Divice

Table III. Sampling Devices used to Establish Boundaries and
Composition of Assemblages

St. Number Djvice

IV. Northern Gulf, Nearshore
Shelf, 11 to 26 meters
24 Van Veen, Orange Peel

1 14 Van Veen grab

172 Shell dredge

175 Shell dredge

181 Shell dredge

184 Shell dredge

185 Shell dredge

190 Shell dredge

191 3-meter otter trawl

194 Shell dredge

195 Shell dredge

196 Shell dredge
208 Shell dredge
212 3-meter otter trawl

14 samples2 Van Veens (1/20 m-)

10 Shell dredges (100 x 30 cm.)
2 3-meter otter trawls

Above stations used in assessing all index
groups shown in Table IV.

I

Rocky Shores

100

Beach collection

101

Beach collection

103

Beach collection

104

Beach collection

105

Beach collection

107

Beach collection

108

Diving

109

Beach collection

115

Beach collection

118

Beach collection

119

Diving

II samples9 beach collection;
2 dives

II. Beaches and Sand Flats
to lOm.

4

Orange peel grab

5

Van Veen grab

7

Orange peel grab

102

Hand collection

106

Beach collection

111

Van Veen grab

112

Minidredge

113

Van Veen grab

114

Van Veen grab

116

Beach collection

117

Beach collection

118

Van Veen, minidn

119

Diving

160

Beach collection

162

Beach collection

163

Beach collection

165

Rock dredge

179

Beach collection

193

Beach collection

205

Beach collection

206

Beach collection

270

Orange peel grab

292

Diving

27 samples 3 orange peels (1/15 m^)
5 Van Veens (1/20 m^)
1 1 Beach collections
2 Minidredges (10 ■- 30 cm.)
2 Diving
1 Rock dredge (30 x 100 cm.)

III. Low Salinity Lagoons
292 Diving

206 Shore collecting

117 Shore collecting

Overall assessment from literature and
personal communications.

171
181
184
190
194
195
196
24
208

Shell dredge
Shell dredge
Shell dredge
Shell dredge
Shell dredge
Shell dredge
Shell dredge
Van Veen grab
Shell dredge

9 samples 8 Shell dredges (100 x 30 cm.)

1 Van Veen (1/15 m^)

Above stations used in obtaining composite
assemblage, figure 17.

IV. Southern Nearshore Shelf,

11 to 26 meters
1 Van Veen grab

5 Van Veen grab

51 a, b, 1/10 m^ Petersen grab
c,d(4)

112 Minidredge

1 13 Van Veen grab

148 3-meter otter trawl

149 3-meter otter trawl
157 3-meter otter trawl

288 Orange peel grab

289 Orange peel grab

13 samples 3 Van Veens (1/20 m^)

4 Petersen grabs (1/10 m^)

2 Orange peels (1/15 m^)

3 3-meter otter trawls

1 minidredge (10 x 30 cm.)

177

Table III (continued)

St. Number Device

V. Northern Intermediate Shelf,
27 to 65 meters

56

Shell dredge

164

3-meter otter trawl

166

Rock dredge

170

Shell dredge

171

Shell dredge

175

Shell dredge

182

3-meter otter trawl

185

Shell dredge

186

Shell dredge

188

Shell dredge

191

3-meter otter trawl

204

Rock dredge

212

3-meter otter trawl

13 samples 7 Shell dredges (100 ;■: 30 cm.)
4 3-meter otter trawls

2 Rock dredges (100 x 30 cm.)

V. Southern Intermediate Shelf,

27 to 65 meters
2 Phleger cores

87 12-meter otter trawl

94 12-meter otter trawl

95 12-meter otter trawl

97 12-meter otter trawl

98 12-meter otter trawl

150 3-meter otter trawl

151 Dipnet

153 Box dredge

154 Box dredge

158 3-meter otter trawl

159 3-meter otter trawl

12 samples 5 12-meter otter trawls

3 3-meter otter trawls

2 Box dredges (100 x 30 cm.)
1 Phleger core (3 cm. diameter)
1 Dipnet

VI

6

50

92
93
147
152

Southern Outer Shelf,
66 to 126 meters

Orange peel grab

Shell dredge

12-meter otter trawl

12-meter otter trawl

Shell dredge

Rock dredge

3-meter otter trawl

Box dredge

8 samples 1 Orange peel (1/15 m-)

2 Shell dredges (100 :■ 30 cm.)

2 12-meter otter trawls

1 3-meter otter trawl

1 Rock dredge (100 x 30 cm.)

1 Box dredge (100 ■: 30 cm.)

St. Number Device

VII. Northern Outer Shelf,
66 to 126 meters

23

Orange peel grab

64

10-meter otter trawl

68

Shell dredge

69

1/10 m- Petersen grab

70

Shell dredge

71

Shell dredge

72

Shell dredge

82

Rock dredge

83

Rock dredge

164

3-meter otter trawl

166

Rock dredge

182

3-meter otter trawl

198

Shell dredge

203

Rock dredge

204

Rock dredge

209

Shell dredge

210

Shell dredge

211

3-meter otter trawl

18 samples 1 Orange peel (1/15 m-)
1 1/10 m- Petersen grab
7 Shell dredges (100 X 30 cm.)
1 10-meter otter trawl
3 3-meter otter trawls
5 Rock dredges (100 x 30 cm.)

VIII.

Northern Gulf Basins

230 to ISOOmeters

18

Orange peel grab

19

Gravity corer

58

Rock dredge

59

Rock dredge

60

Gravity corer

61

Box dredge

62

Rock dredge

63

Box dredge

65

Deep diving dredge

66

Piston corer

67

Piston corer

68

Shell dredge

72

Shell dredge

73

Piston corer

74

Piston corer

75

Piston corer

80

Rock dredge

199

Rock dredge

200

Rock dredge

19 samples 1 Orange peel (1/15 m^)
2 Gravity cores
(4 cm. in diameter)

5 Piston cores (8cm. in diameter)

6 Rock dredges (100 x 10 cm.)
2 Box dredges (100 x 30 cm.)
2 Shell dredges (100 x 10 cm.)
1 Deep diving dredge cutting

edge 1.5 m.

78

St. Number Device

IX.

10
40
43
43
45
53
54
91
99
156
167
168
187
201
202

Upper Slope, Southern and

Central Gulf,

121 to 730meters

Orange peel grab

Rock dredge

Box Dredge

Box Dredge

Box Dredge

Box dredge

Shell dredge

12-meter otter trawl

Rock dredge

3-meter otter trawl

3-meter otter trawl

Shell dredge

Shell dredge

Shell dredge

Shell dredge

14 samples 1 Orange peel (1/15 m'^)

2 Rock dredges (100 v 30 cm.)

3 Box dredges (100 ;■: 30 cm.)
5 Shell dredges (100 / 30 cm.)

1 12-meter otter trawl

2 3-meter otter trawls

Table III (continued)

St. Number Device

XI. Abyssal Southern Basins
and Outer Slope,

1800 to 4122 meters
3 Mid-water trawl (bottom)

39 1 /5 m^ Petersen grab

41 Deep diving dredge

42 Deep diving dredge
52 Deep diving dredge
86 1 /5 m^ Petersen grab
96 12-meter otter trawl

128 Deep diving dredge

131 Deep diving dredge

134 Deep diving dredge

137 10-meter otter trawl

139 10-meter otter trawl

141 10-meter otter trawl

272 5-meter otter trawl

274 10-meter otter trawl

275 10-meter otter trawl

276 10-meter otter trawl

277 3-meter Beam trawl
285 3-meter Beam trawl
287 3-meter Beam trawl

X. Middle Continental Slope,
731 to l,799meters

39 1/5 m^ Petersen grab

40 Rock dredge

84 Deep diving dredge

90 12-meter otter trawl

127 Deep diving dredge

135 Deep diving dredge

138 10-meter otter trawl

214 1 /5 m^ Petersen grab

215 Rock dredge

216 1/5 m^ Petersen grab
221 1/5 m^ Petersen grab

273 5-meter otter trawl

11 samples4 1/5 m- Petersen grabs

3 Deep diving dredges

(cutting edge 1.5 m.)

1 12-meter otter trawl

1 10-meter otter trawl

1 5-meter otter trawl

2 Rock dredges (100 x 30 cm.)

20 samples 1 Mid-water trawl on bottom
(2.5 meters)

2 1 /5 m^ Petersen grabs
6 Deep diving dredges

(cutting edge 1.5 m.)
1 12-meter otter trawl
6 10-meter otter trawls
1 5-meter otter trawls

3 3-meter beam trawl

XII. California Borderland Basins,
1641 to 2358 meters

144 5-meter otter trawl

145 5-meter otter trawl

255 5-meter otter trawl

256 5-meter otter trawl

257 5-meter otter trawl

258 5-meter otter trawl

259 5-meter otter trawl

260 5-meter otter trawl
271 5-meter otter trawl

9 samples 9 5-meter otter trawls

(Siertrykkene udkommet den 17. februar 1964).

PLATES

Plate I.

I. Intertidal and shallow rocky shores assemblage.
Fig.

1. Littorina aspcra Philippi, 1846. Aperture, size - 20 x 13 mm.

2. Nerita scabricosta Lamarck, 1822. Aperture, size - 43 x 40 mm.

3. Turbo fliictuosus Wood, 1828. Aperture, size -31 x 30 mm.

4. Turbo saxosus Wood, 1828. Aperture, size -16x15 mm.

5. Cerithium stercusmuscarum Valenciennes, 1833. Aperture, size - 26 x 11 mm.

6. Vermicularia pellucida (Broderip and Sowerby, 1829). Aperture, size - 16 x 9 mm.

7. Pyrene fuscala (Sowerby, 1832). Aperture, size- 18 x 11 m.

8. Purpura patula pansa Gould, 1852. Aperture, size - 37 x 24 mm.

9. Jenneria pustulata (Solander, 1786). A. Dorsal, B. Aperture, size - 16 x 10 mm.

10. Siphonaria maura Sowerby, 1835. A. Dorsal, B. Interior and animal, size -7-8 mm.

1 1. Arcopsis solida Sowerby, 1833. A. Exterior, B. Interior, size -12x7 mm.

12. Isognomon cheninilzianus (Orbigny, 1853). A. Exterior, B. Interior, size - 33 ■ 23 mm.

13. Cardita affinis californica Deshayes, 1854. A. Exterior, B. Interior, size - 65 x 28 mm.

14. Anomia adamas Gray, 1850. A. Exterior, B. Interior, size -32 x 27 mm.

D. N. F.V. M. Vol 126.

-^

Pl. I

9 a

11 a

10 a

10 b

12a

11 b

13a

13b

12 b

14a

14 b

Plate II.
II. Sand beaches and sand flats to 10 meters.

FiK.

1. Ccrithium maculosum Kiener, 1841. Aperture, size - 45 x 27 mm.

2. Turritella leucosloma Valenciennes, 1832. Aperture, size - 69 x 16 mm.

3. Strombiis gramilatiis Swainson, 1822. Aperture, size - 81 x 40 mm.

4. Oliva incrassata (Solander, 1786). Aperture, size- 60 x 33 mm.

5. Olivella fletcherae Berry, 1958. Aperture, size- 11x4 mm.

6. Bulla gouldiana Pilshry, 1895. Aperture, size - 40 ■ 28 mm.

7. Anadara multicostata (Sowerby, 1833). A. Exterior, B. Interior, size - 53 ■ 46 mm.

8. Anadara labiosa (Sowerby, 1833). A. Exterior, B. Interior, size - 20 x 14 mm.

9. Diplodonta sericata (Reeve, 1850). A. Exterior, B. Interior, size- 10 x 10mm.

10. Tivela byronensis (Gray, 1838). A. Exterior, B. Interior, size - 39 x 33 mm.

11. Megapitaria squalida (Sowerby, 1835). A. Exterior, B. Interior, size- 67 x 54mm.

12. Dosinia dunkeri (Philippi, 1844). A. Exterior, B. Interior, size -61 x 63 mm.

13. Dosinia pondcrosa (Gray, 1838). A. Exterior, B. Interior, size - 123 x 114 mm.

14. Anomalocardia subimbricata lumens (Verrill, 1870). A. Exterior, B. Interior,
size - 29 x 25 mm.

15. Pilar lupanaria (Lesson, 1830). Exterior, size - 26 ■ 20 mm.

16. Heterodonax bimaculalus (Linne, 1758). A. Exterior, B. Interior, size - 26 x 15 mm.

17. Mulinia pallida (Broderip and Sowerby, 1829). A. Exterior, B. Interior,
size - 49 ■ 36 mm.

18. Tellina felix Hanley, 1844. Interior, size -10-5 mm.

19. Donax carinalus Hanley, 1843. Exterior, size - 26 < 15 mm.

20. Donax punctaloslriahis Hanley, 1843. A. Exterior, B. Interior, size - 32 ■: 21 mm.

21. Tagelus affinis (C. B. Adams, 1852). A. Exterior, B. Interior, size - 48 x 18 mm.

D.N. F. V. M. Vol. 126.

PL. II

Plate III.

III. Lagoons and mangrove swamps.
Fig.

1. Littoridina, sp. Aperture, size -3-2 mm.

2. Cerithidea mazatlanica Carpenter, 1856. Aperture, size - 26 ■ 11 mm.

3. Cerithidea montagnei (Orbigny, 1837). Aperture, size - 30 > 17 mm.

4. Anadara tuberculosa (Sowerby, 1833). A. Exterior, B. Interior, size - 65 x 45 mm.

5. Crassostrca corteziensis Hertlein, 1951. A. Exterior, B. Interior, size - 80 x 45 mm.

6. Crassostrea columbiensis Hanley, 1846. Interior, size -45 x 50 mm.

7. Crassostrea corteziensis Hertlein, 1951. Interior, size - 126 x 60 mm (large example).

8. Polymesoda olivacea (Carpenter, 1855). A. Exterior, B. Interior, size -21 x 18 mm.

9. Polymesoda mexicana (Broderip and Sowerby, 1829). A. Exterior, B. Interior,
size - 42 :■: 43 mm.

D. N. F. V. M. Vol. 126.

PL. Ill

s

4 a

>^

y

5 a

5 b

8 a

8 b

9 b

Plate IV.

IV. Nearshore shelf, 1 1-26 meters.
Fig.

1. Architedonica nobilis Roding, 1798. Aperture, size- 10 ■ 21 mm.

2. Cnicihuliim spinosum (Sowerby, 1824). Exterior, size 17 • 14 mm.

3. Natica broderipiana Recluz, 1844. Aperture, size - 24 > 23 mm.

4. Polinices reclusianus (Deshayes, 1839). Aperture, size - 24 x 25 mm.

5. Polinices otis (Broderip and Sowerby, 1829). Aperture, size - 10 ■ 10 mm.

6. Sinum debile (Gould, 1853). Aperture, size - 8 > 2 mm.

7. Hexaplex erythrostomus (Swainson, 1831). Aperture, size -95 x 71 mm.

8. Hexaplex brassica (Lamarck, 1822). Aperture, size -79 x 58 mm.

9. Strombus gracilior Sowerby, 1825. Aperture, size - 67 x 47 mm.

10. Nassarius versicolor (C. B. Adams, 1852). Aperture, size -9 x 5 mm.

1 1. Oliva spicata (Roding, 1798). Aperture, size - 32 x 17 mm.

12. Mitra erythrogramma Tomlin, 1931. Aperture, size -17x6 mm.

13. Hormospira maculosa (Sowerby, 1834). Aperture, size -45 x 14 mm.

14. Anadara obesa (Sowerby, 1833). A. Exterior, B. Interior, size- 22 x 16mm.

15. Anadara mix (Sowerby, 1833). A. Exterior, B. Interior, size- 19 x 17 mm.

16. Adrana penascoensis (Lowe, 1935). Exterior, size - 16 ■ 5 mm.

17. Modiolus eiseni Strong and Hertlein, 1937. Exterior, size - 17 ■ 12 mm.

18. Crassatella gibbosa Sowerby, 1832. A. Exterior, B. Interior, size - 30 x 18 mm.

19. Trigoniocardia granifera (Broderip and Sowerby, 1829). Exterior, size -8x7 mm.

20. Trachycardium panamense (Sowerby, 1833). Exterior, size - 18 :■ 18 mm.

21. Chlamys tumbezensis (Orbigny, 1846). A. Exterior, B. Interior, size- 15 x 14 mm.

22. Chlamys circularis (Carpenter, 1864). A. Exterior, B. Interior, size - 33 x 30 mm.

23. Laevicardium elenense (Sowerby, 1840). Exterior, size- 13 x 12 mm.

24. Mactra californica Conrad, 1837. Exterior, size - 33 x 23 mm.

25. Pilar concinnus (Sowerby, 1835). A. Exterior, B. Interior, size - 24 ■ 17 mm.

26. Chione mariae (Orbigny, 1846). Exterior, size - 30 x 20 mm.

27. Pandora claviculata Carpenter, 1856. A. Exterior, B. Interior, size - 30 x 12 mm (Broken).

28. Tellina arenica Hertlein and Strong, 1949. Exterior, size -13x8 mm.

29. Donax gracilis Hanley, 1845. A. Exterior, B. Interior, size- 18 ■ 7 mm.

30. Lyonsia gouldii Dall, 1915. Exterior, size -13x6 mm.

D.N. F.V. M. Vol. 126.

PL. IV

25 b

29 b

Plate V.

V. Intermediate shelf, 27 to 65 meters.
Fig.

1. Calliostoma bonita Strong, Hanna, and Hertlein, 1933. Aperture, size - 20 - 21 mm.

2. Astele rema (Strong, Hanna, and Hertlein, 1933). Aperture, size - 9 x 12 mm.

3. Solariella triplostephanus Dall, 1910. Aperture, size -6x7 mm.

4. Architedonica placentalis (Hinds, 1844). Aperture, size -8x19 mm.

5. Polinices uber (Valenciennes, 1832). Aperture, size - 16 x 12 mm.

6. Cassis centiqiiadrata (Valenciennes, 1832). Aperture, size -42 x 32 mm.

7. Distorsio dccussatiis (Valenciennes, 1832). Aperture, size -47 x 25 mm.

8. Bursa californica sonorana Berry, 1960. Aperture, size - 51 x 36 mm.

9. Bursa nana (Broderip and Sowerby, 1829). Aperture, size - 50 x 30 mm.

10. Murex recurvirostris Broderip, 1833. Aperture, size -43 x 23 mm.

11. Eupleura nmriciformis (Broderip, 1833). Aperture, size -26 x 16 mm.

12. Cantharus, n. sp. Aperture, size - 37 > 24 mm.

13. Fusinus dupetitthouarsi {Kiener, 1846). Aperture, size - 79 :■ 25 mm.

14. Mitra hindsii Reeve, 1844. Aperture, size - 24 x 8 mm.

15. Harpa crenata Swainson, 1822. Aperture, size - 34 > 21 mm.

16. Claims roseolus (Hertlein and Strong, 1955). Aperture, size - 17 • 7 mm.

17. Pleuroliria picta (Reeve, 1843). Aperture, size - 36 x 1 1 mm.

18. Anodontia edcntuloides (Verrill, 1870). A. Exterior, B. Interior, size - 40 ;■ 37 mm.

19. Trachycardium bckheri (Broderip and Sowerby, 1829). A. Exterior, B. Interior,
size - 29 ■ 30 mm.

20. Eucrassatella gibbosa forma rudis Sowerby, 1832. A. Exterior, B. Interior,
45 X 28 mm.

21. Tellina pristiphora Dall, 1900. A. Exterior, B. Interior, size -38 x 28 mm.

22. Semele paziana Hertlein and Strong, 1949. A. Exterior, B. Interior, size -27x21 mm.

23. Nemocardium paziamim (Dall, 1916). Exterior, size- 11 ■ 10 mm.

D.N. F.V. M. Vol. 126.

PL. V

10

r/

16 ' 17

20 a

20 b

"^^

'■^

11

1»

13

"

14

15

19a

18 a 18 b

*i

..«^'**%lv

i#

9

■i \

21 a

%4ii^»

22 a 19 b

21 b 22 b

23

Plate VI.

\'I. Outer shelf, southern gulf, clay bottom, 66-1 20 meterr.
Fig.

1. Crucibiilum, n. sp. A. Exterior, B. Interior, size -31 -27 mm.

2. Nassarius catallus Dall, 1908. Aperture, size - 17 :■ 10 mm.

3. Conus arcuatus Broderip and Sowerby, 1829. Aperture, size - 40 ■ 20 mm.

4. Anadara mazatlanica (Hertlein and Strong, 1943). A. Exterior, B. Interior,
size - 42 V 27 mm.

5. Chione kellettii (Hinds, 1845). A. Exterior, B. Interior, size -53 x 43 mm.

6. Pitar mexicamis Hertlein and Strong, 1948. A. Exterior, B. Interior, size - 50 x 40 mm.

7. Periploma carpcnteri Dall, 1896. A. Exterior, B. Interior, size - 30 x 42 mm.

VII. Outer shelf, northern gulf, sand bottom, 66-1 20 meterr.

8. Polinices intenieratus (Philippi, 1853). Aperture, size -9 ;■ 9 mm.

9. Strombus graniilatus Swainson, 1822. (Pliocene?). Aperture, size - 69 ■ 43 mm.

10. Cymatium amidum (Reeve, 1844). Aperture, size - 34 x 18 mm.

11. Pleuroliria nobilis (young) (Hinds, 1843). Aperture, size -32 x 17 mm.

12. Pleuroliria oxytropis (Sowerby, 1834). Aperture, size -19x6 mm.

13. Glycymeris fessellata (deep form) (Sowerby, 1833). Exterior, size - 25 > 25 mm.

14. Lucinonuj ammlata (Reeve, 1850). A. Exterior, B. Interior, size - 43 > 38 mm.

15. Nemocardiuru centifilosum (Carpenter, 1864). A. Exterior, B. Interior, size - 10 ■ 9.5 mm.

16. Macorna lamproleuca (Pilsbry and Lowe, 1932). A. Exterior, B. Interior, size - 36 ;■ 21 mm.

17. Corbula ventricosa Adams and Reeve, 1850. Exterior (whole), size- 11 x 7mm.

D.N. F.V. M. Vol. 126.

Pl. VI

m

'm.

m

1 a

1 b

4 a

4 b

5 a

5 b

.^^

6 b

7 b

Plate VII.

VIII. Deep northern basins and troughs, 230-1,500 meters.
Hiu.

1. Tiirriti'lla, sp. Aperture, size - 37 ■ 10 mm.

2. Boreotrophon, n. sp. .Aperture, size - 40 x 19 mm.

3. Fiisiniis traski Dall, 1915. Aperture, size -43 >; 15 mm.

4. Acila castrensis Hinds, 1843. Exterior, size- 11 x 10mm.

5. Nuculana taphria (Dall, 1897). Exterior, size -13x8 mm.

6. Nuculana hamata Carpenter, 1864. A. Exterior, B. Interior, size - 1 1 -6 mm.

7. Glycymeris cortezianus (Dall, 1901). A. Exterior, B. Interior, size - 19 > 8 mm.

8. Cardita harbarensis (Stearns, 1890). A. Exterior, B. Interior, size- 17 x 15 mm.

9. Lucina tenuisculpta (Carpenter, 1864). A. Exterior, B. Interior, size -8 x 7.5 mm.
10. Hiatdla ardica (Linne, 1767). A. Exterior, B. Interior, size- 11 • 6mm.

IX. Upper slope, central and southern gulf, 1 2 1-730 meters.

11. Pundurella expansa Dall, 1896. A. Exterior, B. Interior (animal), size - 23 x 20 mm.

12. Solariella permabilis Carpenter, 1864. Aperture, size -7-9 mm.

13. Nassarius insculptus gordanus Hertlein and Strong, 1951. Aperture, size - 22 >: 12 mm.

14. Nassarius miser (Dall, 1908). Aperture, size - 12 x 7 mm.

15. Clathurdla thalassoma (Dall, 1908). Aperture, size -22 x 8 mm.

16. Nucula cardara Dall, 1917. Exterior, size -10x7 mm.

17. Cydopeden zacae (Hertlein, 1935). Exterior, size - 8 ' 7 mm.

D.N. F. V. M. Vol. 126.

PL. VII

2

1^

\ 3

s^

6 a

7 a

8 a

y^^.

V.

-"Tb ''

11 a

12

13

n b

15 16

14

17

Plati£ VIII.

X. Middle slope, 731 to 1,799 meters.
Fig.

1. Cocculina diomedca Dall, 1908 (?). Exterior, size -9 .-; 6 mm.

2. Turcicula bairdii Dall, 1889. Aperture, size - 44 x 41 mm.

3. Solariella nuda Dall, 1896. Aperture, size - 10 x 13 mm.

4. Solemya agassizi Dall, 1908. A. Exterior, B. Interior, size -42 x 18 mm.

5. Vesicomya lepta Dall, 1896. A. Exterior, B. Interior, size -45 x 33 mm.

XII. California borderland basins, 1,641 to 2,358 meters.

6. Coins halidonus Dall, 1919. Aperture, size -34 x 20 mm.

7. Coins of. halli Dall, 1873. Aperture, size - 34 x 20 mm.

8. Coins trophius Dall, 1919. Aperture, size - 29 x 16 mm.

9. Ancistrolepis magnus Dall, 1894. Aperture, size - 60 x 46 mm.

10. Buccimim diplodetum Dall, 1907. Aperture, size - 16 x 11 mm.

1 1. Chrysodomus liratus Martyn, 1784. Aperture, size - 67 x 37 mm.

12. Antiplanes vinosa Dall, 1874. Aperture, size - 27 ■' 13 mm.

13. Solemya of. johnsoni Dall, 1891. A. Exterior, B. Interior, size - 65 ■ 30 mm.

14. Malleliafaba Dall, 1897. A. Exterior, B. Interior, size- 18 x 11 mm.

15. Cyclopeden randolphi tillamookensis (Arnold, 1906). Exterior, size - 23 x 23 mm.

16. Chlamys latiaurata monotimeris (Conrad, 1837). Exterior, size - 23 x 23 mm.

17. Vesicomya stearnsi Dall, 1895. A. Exterior, B. Interior, size - 45 ~- 33 mm.

D. N. F. V. M. Vol. 126.

PL. VIII

4 b

11

af

%

12

:*/

5 a

5 b

y % *

»# w

10

14 a

13a

*»*«i«^ •

13 b

14b

15

16

17 a

17 b

Plate IX.

XI. Abyssal southern borderland basins and lower slope,
1,800 to 4,122 meters.
Fig.

1. Chitinous gastropod (?). A. Aperture, B. Back, size - 50 ;•; 35 mm.

2. Solariella ceratophora Dall, 1896. Aperture, size -21 x 19 mm.

3. Solariella eqiiatorialis Dall, 1908. Aperture, size - 23 x 20 mm.

4. Fusinus nifocaiidatus Dall, 1896. Aperture, size - 40 x 1 1 mm.

5. Tradolira sparta Dall, 1896. Aperture, size - 19 ■ 9 mm.

6. Pleurotomella clarinda Dall, 1908. Aperture and animal, size - 67 ■ 29 mm.

7. Steiraxis anlaca Dall, 1896. Aperture, size -52 >: 21 mm.

8. Turris (Gemnmla) sp. (see Dall, 1889). Aperture, size -42 x 29 mm.

9. Solemya agasski Dall, 1908. A. Exterior, B. Interior, size- 42 x 18 mm.

10. Nucula panamina Dall, 1908. A. Exterior, B. Interior, size- 15 x 10 mm.

11. Nuciilana agapea (Dall, 1908). A. Exterior, B. Interior, size -21 > 12 mm.

12. Tindaria compressa Dall, 1908. A. Exterior, B. Interior, size - 10 >: 8 mm.

13. Limopsis compressus Dall, 1908. A. Exterior, B. Interior, size - 29 x 20 mm.

14. Area eorpulenta pompholynx Dall, 1908. A. Exterior, B. Interior, size - 25 x 29 mm.

15. Area cf. mieleator Dall, 1908. A. Exterior, B. Interior, size- 14 x 15 mm.

16. Abra profundorum E. A. Smith, 1885. Exterior (Broken, whole), size - 20 x 13 mm.

17. Cuspidaria panamensis Dall, 1908. Exterior, size - 42 x 25 mm.

18. Myonera garretti Dall, 1908. Exterior, size -21 x 15 mm.

19. Poromya perla Dall, 1908. Exterior (whole), size - 18 x 17 mm.

D.N. F.V. M. Vol. 126.

PL. IX

14b

Plate X.

Some bathyal and abyssal mollusks illustrated by artist Poul Winthcr
of Copenhagen, Denmark.
Fit;.

1. Enuirginula relascoensis Shasky, 1961. Upper slope.
A. Side view, B. Top, C. Interior with animal.

2. Chitonous gastropod (?). Abyssal southern borderland. Aperture (see Plate IX).

3. Steiraxis aulaca Dall, 1896. Abyssal southern borderland. Aperture (see Plate IX).

4. Fusimis rufocaudatus Dall, 1896. Abyssal southern borderland, (see Plate IX).

5. Turris (Gemmula), sp. Abyssal southern borderland, Aperture (see Plate IX).

6. Solemya agassizi Dall, 1908. Abyssal southern borderland. A. Whole live specimen, with
undescribed hydroid attached to one end, B. Interior (see Plate IX).

7. Solemya valvulus Carpenter, 1864. Upper slope. Whole live specimen.

D. N. F.V. M. Vol. 126.

I'

PL. X

Plate XI.

Abyssal holothurian, probably in the family Psychropotidae, photographed on the bottom

in 3550 meters at 28 56' N. Lat., 117 30'W. Long., Guadalupe Basin near Biology Station

276, off Punta Eugenia, Baja California. Courtesy Dale F. Krause.

D. N. F. V. M. Vol. 126.

PL. XI

Plate XII.

Photograph of bottom at a depth of 1935 meters at 31 19' N. Lat., 117-28'W. Long, off
Cabo Colnett, Baja California, a few miles from Biology Station 137. Appearing in area of
about 2 square meters are three ophiuroids, a 6 inch long holothurian, two large chitonous
tube-forming polychaetes, and a possible Antipitharian. Most of these were taken in the
nearby trawl. Courtesy Dale F. Krause.

D.N. F.V. M. Vol. 126.

PL. XII

Plate XIII.

Photograph from same area as Plate XII., off Cabo Colnett. Shown here in less than 2

square meters are one Hexactinelid sponge, two ophiuroids, one fish ad 4 polychaetes.

Note tracks of armoured polychaetes. Courtesy Dale F. Krause.

D. N. F.V. M. Vol. 126.

Pl.XIII

Plate XIV.

Same station as Plate XIII. Area less than one square meter. Note polychaete extending

out of tube. Munid crab (possibly Munidopsis bairdii), apparently clinging to glass sponge,

and ophiuroid in left-hand corner. Courtesy Dale F. Krause.

D.N. F.V. M. Vol. 126.

Pl. XIV

Y
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Plate XV.

A. Sea bottom near same station 137 in Animal Basin off Cape Colnett, 1935 meters. Area
about 3 square meters. Note 4 large ophiuroids, 3 tubed-polychaetes, and numerous large

burrows. Courtesy Dale F. Krause.

B. Enlargement of polychaete in Plate XIV. Note signs of intense bottom activity,
consisting of tracks, holes, and general disturbance. Courtesy of Dale F. Krause.

D.N. F.V. M. Vol. 126.

Pl. XV

^ -m, ^0"