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Musée national des sciences naturelles National Museum of Natural Sciences
Publications en zoologie, n° 2 Publications in Zoology, No. 2
On Acroloxus coloradensis (Henderson)
(Gastropoda, Basommatophora)
in Eastern Canada

by Arthur H. Clarke |

Musées nationaux du Canada National Museums of Canada

1970

Digitized by the Internet Archive
in 2011 with funding from
California Academy of Sciences Library

http://www.archive.org/details/publicationsinzo21 nati

ON ACROLOXUS COLORADENSIS (HENDERSON)
(GASTROPODA, BASOMMATOPHORA)
IN EASTERN CANADA

CANADA

National Museum of Natural Sciences
Musée national des sciences naturelles

Publications in Zoology, No. 2
Publications en zoologie, n° 2

Issued under the authority of
the National Museums of Canada

Publié avec l'autorisation des
musées nationaux du Canada

ON ACROLOXUS COLORADENSIS (HENDERSON)
(GASTROPODA, BASOMMATOPHORA)
IN EASTERN CANADA

by Arthur H. Clarke

Ottawa 1970

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Contents

Résumé, vi
Summary, vi
Introduction, 1
Acknowledgments, 3
Collecting sites, 4
Habitats, 5

The shell, 8

The living animal, 9
Zoogeography, 11
Addenda, 12
Literature cited, 13

List of Figures

1 Two views of a preserved specimen of Acroloxus coloradensis from
Lac Gabrielle, Quebec, 3

2 A general view of station 946 at Lac Caché, Quebec, 5

3 A closer view of the microhabitat at station 946, 7

Résume

On a découvert récemment, au Centre-Nord du Québec et au Nord-Est de
l'Ontario, une patelle (Acroloxus coloradensis) dont on n’avait jusqu'ici constaté
la présence que dans quatre lacs des montagnes Rocheuses. On en rencontre
des populations éparses sur des roches et sur des coquilles vides d’Anodontes,
dans les eaux peu profondes qui bordent la rive de certains lacs mésotrophes.
Le présent ouvrage donne quelques détails d'écologie, ainsi que des observations
sur la morphologie des adultes et de l’enveloppe des oeufs. On y trouvera enfin
des remarques sur la zoogéographie de ce mollusque et sur une présumée relation
entre les coquilles de moules et les patelles d’eau douce.

Summary

Acroloxus coloradensis, a limpet previously known only from four lakes in
the Rocky Mountains, has been discovered in north-central Quebec and north-
eastern Ontario. Sparse populations occur on cobbles and on empty Anodonta
shells in shallow near-shore habitats in mesotrophic lakes. Observations on
ecology and on the morphology of egg capsules and adults are presented. Also
included are remarks on zoogeography and on a presumed relationship of mussel
shells and freshwater limpets.

Vi

Introduction

The Superfamily Acroloxacea (freshwater limpets) contains one Family
(Acroloxidae), one Genus (Acroloxus), and seven living species, six in
Eurasia and one in North America. The group exhibits many unique features
of cytology, reproduction, and anatomy, especially the dextral organization of
the organs, which sets them apart from other higher Basommatophora, i.e.,
the Lymnacea and Ancylacea (see Hubendick 1962; Bondesen 1950; Burch
1962). Shell characters are also unique, particularly the prominent, extended,
and (in some species) acutely pointed apex, located posteriorly and on the
left. In Ancylidae, the major family of freshwater limpets, the apex is also
principally posterior but in the midline or on the right.

Acroloxidae are recorded from deposits as old as Upper Cretaceous in
Europe (subgenus Pseudancylastrum Lindholm) and Paleocene in North
America (Palaeancylus Yen). The Recent Eurasian species are — Acroloxus
lacustris (L.), found throughout Europe and northern Asia; A. improvisus
(Polinski) and A. macedonicus (Hadzisce), endemic in Lake Ochrid, Yugo-
slavia; and A. (Pseudancylastrum) kobelti (Dybowski), A. (P.) sibiricum
(Gerstfeldt, and A. (P.) troscheli (Dybowski), endemic in Lake Baikal,
U.S.S.R.

The single North American Recent species, Acroloxus coloradensis
(Henderson), is apparently rare and has been recorded alive from only four
lakes, all high in the Rocky Mountains. These are — Eldora Lake, Boulder
County, Colorado, collected by Junius Henderson in 1925; Lake Iris and
“lake north of Geikie Station,” both in the Miette Valley, Jasper National
Park, Alberta, collected by Alan Mozley in 1925 and 1926 (see Basch 1963);
and Lost Lake, Glacier National Park, Montana, collected by R. H. Russell
and R. B. Brunson in 1966 (see Russell and Brunson 1967) and by R. H.
Russell in 1968. A. coloradensis is also known from Pleistocene deposits of
Nebraskan or Aftonian age in Brown County, Nebraska and Kingman County,
Kansas (Taylor 1960: 61).

While studying freshwater molluscs collected from 1959 to 1967 in
connection with another work I was much surprised to find Acroloxus colora-
densis among an unsorted collection of freshwater limpets. Two preserved
specimens with soft parts and one empty shell were present. According to
field notes these had been collected in 1960 from a lake in north-central
Quebec and from a pond in northeastern Ontario, respectively. These loca-
tions are about 1600 and 1340 mi. distant from Eldora Lake, Colorado, the
closest and most easterly Recent locality previously known.

As soon as weather would permit, in June 1968, another trip was made
to north-central Quebec with the hope of confirming the presence of A.
coloradensis there. The effort was a success. Living Acroloxus were found
at two additional localities, ecological observations were made, and living
specimens were brought back to the laboratory for observation.

Acknowledgments

My assistant, Mrs. M. F. I. Smith, helped greatly in our efforts to culture
A. coloradensis in the laboratory and assisted in several other ways. Com-
parative specimens of A. coloradensis from Alberta and Montana were
generously made available by Dr. R. Tucker Abbott, Philadelphia Academy
of Natural Sciences, and by Richard H. Russell, University of Arizona. The
algae were identified by Dr. R. K. Lee, Curator of Algology; the Hirudinea
by Mrs. Fahmida Rafi, Assistant in Invertebrate Zoology (both of the
National Museum of Natural Sciences); and the Trichoptera by Dr. F.
Schmidt, Entomology Research Institute, Canada Department of Agriculture.
Mr. Benjamin Korda, Department of National Health and Welfare, took the
excellent photographs of Acroloxus coloradensis used in Figure 1. Field and
laboratory work by the author were supported by the National Museum of
Natural Sciences, National Museums of Canada.

FIGURE 1—Two views of a preserved specimen (NMC 22323) of Acroloxus
coloradensis from Lac Gabrielle, Quebec (station 115). Length 4.7 mm.

Collecting Sites

The eastern Canadian localities that yielded Acroloxus are as follows.
Precise locations for the Quebec sites are taken from National Topographic
Series Map 32G, Edition 2ASE, Series ASO1 (scale 1:250,000) and for the
Ontario site from Map 42A/8 west, Edition 1ASE (scale 1:50,000), both
published by the Department of Energy, Mines and Resources, Surveys and
Mapping Branch, Ottawa, Canada.

Station 115. Lac Gabrielle, the northern bay of the lake near provincial
highway 58, about 10 mi. S. of Chibougamau, Quebec. Precise location:
lat. 49°47’38’N, long. 74°25’32”W, elevation 1,246 ft. Two living specimens
from rocks, July 17, 1960.

Station 177. Unnamed pond, 6 mi. S. of Matheson, Ontario. Precise
location: lat. 48°27’30’N, long. 80°29’10’W, elevation about 1,125 ft. One
empty shell among debris, August 29, 1960.

Station 946. Lac Caché, south half of lake, at rocky point 4 mi. N of
Fecteau Air Base, within sight of highway 58 and about 8 mi. (by road) S.
of Chibougamau, Quebec. Precise location: lat. 49°49’42’N, long. 74°25’-
16’”W, elevation about 1,260 ft. Three living specimens from a water depth
of about 12 in. and 4 to 6 ft. from shore, two from empty Anodonta shells,
and one from a 4-inch rock, June 17, 1968.

Station 947. Lac Doré, north half of lake, about 4 mi. due SE of
Chibougamau. Precise location: lat. 49°52’50’’N, long. 73°16’30”W, eleva-
tion 1,246 ft. One living specimen from a 6-inch rock in about 112 ft. of
water and about 3 ft. from shore, June 18, 1968.

Habitats

Station 115 was not revisited in 1968 because it had been altered during road
improvement. Other localities in the vicinity (stations 946, 947, and several
found to be unproductive) were therefore searched. Station 177 and its
vicinity are yet to be revisited.

Station 946 is at the edge of a small, rounded, exposed rocky point
within an open bay in Lac Caché — an irregular, C-shaped, mesotrophic lake
of about 2 sq. mi. in area. The habitat is shown in Figures 2 and 3. The

FIGURE 2—A general view of station 946 at Lac Caché, Quebec, photographed
on June 17, 1968. The dominant terrestrial plants shown are Labrador
Tea (Ledum groenlandicum) along the shore and Black Spruce (Picea
mariana) with some Eastern White Cedar (Thuja occidentalis) on
higher ground.

three Acroloxus specimens represent the total number that could be found by
examining all movable submersed rocks (about 200) and all empty Anodonta
shells (about 150 valves) seen in the area in depths of from about 6 in. to
212 ft. and at distances of about one to 10 ft. from shore. The submersed rock
and shell surface areas examined are estimated to total about 12 sq. metres.

There are no submersed vascular plants at this station. Rocks at the
2-foot depth are coated with algae, however; and this algae (as later observed
in the laboratory) is fed upon by Acroloxus. This algal community is domi-
nated by the blue-green algae Tolypothrix. Oscillatoria is also abundant, and
some Calothrix (both blue-green algae) also occurs along with isolated uni-
cellular green algae (Chlorococcales) and diatomes (Cymbellacea). The
mussel shells serve as substrate for small colonies of unicellular blue-green
algae (Chroococcacea).

Surface water temperature at noon, June 17, at station 946 was 16°C.
Alkalinity and chlorinity were found’ to be 35 p.p.m. (as CaCO0,) and 15
p.p.m. (as NaCl), respectively.

Station 947, an exposed rocky area along the shore of Lac Doré, is
ecologically very similar to station 946 at Lac Caché. Lac Doré is large,
elongate, and mesotrophic and varies between 12 and 1 mi. in width over its
30-mile length. The shore and shelf at station 947 is composed principally of
boulders and cobbles. Submersed vascular plants are absent, and algae coats
the rocks in shallow water. This algae is similar in colour and macroscopic
appearance to that at station 946. The boulder-cobble shelf is more gently
sloping than that at station 946; about 25 ft. from shore the water is only 3
ft. deep. No mussel shells were seen. The surface area of submersed boulders
and cobbles examined is estimated to be about 6 sq. metres.

Analysis of water quality at station 947 produced results for alkalinity
and chlorinity that were identical to those at station 946.

Stations 115 and 947 are about 10 mi. apart, and station 946 is between
them. All are on connected bodies of water that are adjacent to and con-
fluent with Lac Chibougamau, a major lake in the Nottaway River System.
Station 177 is approximately 275 mi. WSW of the Lac Chibougamau area
and is in the Moose River System. The Nottaway and the Moose river systems
are divergent and are separated by the Harricanaw River System, all three of
which flow into the southern end of James Bay.

Stations 115 and 177 were sampled for all available mollusc species,
and the collections were made from several microhabitats. Stations 946 and
947 were examined specifically for Acroloxus and associated organisms
occurring in the same microhabitat. A meaningful list of associated molluscan
species therefore can only be given for the two latter stations. This is pre-
sented in Table I.

TA Hach water analysis kit was used, Model 39-AP, manufactured by the Hach Chemical
Company, Ames, Iowa.

TABLE 1—Associated Epifaunal Molluscs

Station 946 Station 947
Total Spec./M?| Total Spec./M?

Species | Specimens Specimens

fee +
Acroloxus coloradensis (Henderson) .......... | 3 0.25 1 0.17
PAIN GOLGRIUTOSAN( SAY) EE Te = = ! 0.17
RERIS SIDA ali lAI(S AN) eee eee mr ee = = 2 0.33
Gi ranlisiGeflechisl(Say) Menon aie 11 0.92 1 0.17
BAS EIA: (SES) 8 ho nancoesenuceaucooodoDT 21 0.08 2 0.33
OLIS A ce ge 15 1225 7 1.17

Other associated epifaunal macro-invertebrates were as follows:

Station 946. Trichoptera: Helicopsyche borealis Hagen (pupae and
larvae) and Limmephilus submonilifer Walker (?) (larvae).

Station 947. Hirudinea: Nephelopsis obscura Verrill, Glossiphonia
complanata L., and G. stagnalis L. Trichoptera: Helicopsyche
borealis Hagen (pupae and larvae), Limnephilus (sp.?) (larval
cases) and Psilotreta indecisa Walker (pupae).

\ j a:
rer
>

s ‘ eer Ci ii LÉ À À:

FIGURE 3—A closer view of the microhabitat at station 946 (Lac Caché) in which
the Acroloxus coloradensis were collected. The three large boulders in
the centre are each about 24 inches long and are submerged in about
12 inches of water. A few empty Anodonta shells are faintly visible
in the top centre of the picture.

The Shell

Ancylus coloradensis Henderson, 1939 (now Acroloxus) was proposed as a
replacement name for Ancylus hendersoni Walker, 1925, preoccupied by
Ancylus hendersoni Walker, 1908. Walker’s 1925 description of a specimen
from Eldora Lake, Colorado, is as follows:

“Shell oval, slightly wider anteriorly, very much depressed, light horn
color; anterior and posterior margins regularly rounded, lateral margins about
equally curved, the right somewhat more than the left; anterior, posterior and
right lateral slopes straight, left lateral slope slightly incurved; apex very acute,
almost spine-like, eccentric, turned towards the left side, situated at about
= of the length from the posterior margins and at about 4 of the width
from the left margin, radially striate, the striae continuing over the surface of
the shell from the apex to the margins; surface with fine and regular lines of
growth and delicately radially striate.

Length 5, width 3, alt. 1 mm.” (Walker 1925: 1).

The specimens collected in eastern Canada match this description very
closely. They are also similar to specimens of A. coloradensis collected near
Geikie Station, Alberta, by Alan Mozley in 1926 (ANSP 152666) and to
specimens collected in Lost Lake, Montana, by R. H. Russell in 1968 (NMC
47401). Measurements of the eastern Canadian specimens (in mm) are
given in Table II.

TABLE I]—Measurements

Length Width Height L/W L/H W/H A-PM/L! | A-LM/W!

— 4

Pond 6 mi. S of Matheson, Ont. (Sta. 177, NMC 22322):
4.5 3.0 1.0 15 4.5 3.0 27 57

IL

Lac Gabrielle, 10 mi. S of Chibougamau, Que. (Sta. 115, NMC 22323):

4.7 257 its ed 3.9 22, si .28
5.0 29 1.1 1,7 4.5 2.6 .34 .28

Nm

Lac Caché, 8 mi. S of Chibougamau (Sta. 946, NMC 47402):

3.3 1.8 0.7 1.8 4.7 2.6 21 .39

32 1.9 0.7 JT) 4.6 Da | .28 .32
Lac Doré, 4 mi. SE of Chibougamau (Sta. 947, NMC 47403):

46 | 29 1.2 1.6 3.8 24° | 7,28 | 9338

1A-PM is the distance from the apex to the posterior extremity measured parallel to the midline
of the aperture. A-LM is a similar measurement taken from the apex to the left marginal extremity
and perpendicular to A-PM.

8

The Living Animal

One of the four Acroloxus collected on June 17 and 18 was lost, but the
other three and two Ferrissia parallela from station 947 were carried alive to
Ottawa. On June 22 they were installed in two Petri dishes, which were
three-quarters filled with water from Lac Doré. All limpets from station 946
were placed in one dish, and those from station 947 in the other. A small
algae-covered stone from Lac Caché was also placed in each dish along with
a piece of Anodonta shell from that locality.

Acroloxus coloradensis was seen to move slowly, about hatf as rapidly
as Ferrissia parallela. Both species moved away from strong light, but neither
appeared to be predominantly nocturnal. All the limpets ranged freely over
the immersed surfaces of the dish, stone, and Anodonta shell, the mouth and
radula in constant feeding activity. Much time was also spent immobile, often
on the stone or the shell.

When in motion A. coloradensis does not protrude beyond the edge of
its shell. Some of the anatomy is visible through the translucent, horn-coloured
shell, i.e., a continuous, prominent blackish band along the mantle edge, close
to the shell margin, the orange to brownish-purple visceral mass (there is
colour variation between specimens), the dusky head, and the two black eyes.
Viewed from beneath, the dark mantle band is seen to bear approximately
100 small, bright blue, elongate processes (apparently papillae) lying across
the mantle band and directed toward the mantle edge. The foot and head are
of moderate width, flecked with grey on a pale purplish-brown background,
and not unlike the foot and head of a Ferrissia parallela from Lac Doré. In
general the body appears similar to that of Acroloxus lacustris as figured by
Hubendick (1962, Figure 3).

On the fourteenth day after installation in Petri dishes the large
Acroloxus from station 947 (Lac Doré) deposited one oval egg capsule on
the side of the dish. The egg capsule measured 3.4 x 3.0 mm and contained
three elliptical eggs, 1.2, 1.1, and 1.0 mm long. The adult died on the same
day. From the fourteenth to nineteenth days the two smaller specimens from
station 946 deposited two and three egg capsules respectively, each containing
two or three eggs. These adults died on the twenty-seventh day. Some of the
embryos in the egg masses grew for a few days, but none completed
development.

Although detailed observations of the A. coloradensis egg masses were
not made, the following rather superficial comments may be of some value.
The capsules were lenticular-ovate, from 1.9 to 3.4 mm long, with double
transparent walls and pale yellow lumen, and with two or three eggs in each
capsule. The eggs, which measured from 0.5 x 0.8 to about 0.6 x 1.2 mm,
were ovate and colourless or faintly whitish. The egg capsules and eggs
resemble those of Acroloxus lacustris figured by Bondesen (1950: 64) in
general shape and in that the eggs are loosely packed. They appear to differ in
having yellow lumen (not mentioned for A. lacustris) and a smaller number

9

of eggs in each capsule. Surface striae of the capsules, as mentioned for A.
lacustris by Bondesen, were not observed through the walls of the dishes.

A short statement on the observed behaviour of Ferrissia parallela is also
appropriate. One of the F. parallela from station 947 died on the day of
installation in the Petri dish, but the other remained active. Between the
seventh and eleventh days after installation, it deposited eight egg capsules on
the sides of the dish. It was then transferred to another dish, where it
deposited a few additional capsules before it died on the twenty-fifth day.
The egg capsules contained from one to three closely packed eggs, about the
same size and colour as the Acroloxus eggs. The outer capsule membrane in
Ferrissia was much more closely appressed to the eggs than in Acroloxus,
and the lumen was white, not yellow. Embryonic development proceeded
rapidly, and about five days after ovoposition young Ferrissia, each about 1.0
mm long, began to emerge.

The scanty available evidence indicates that under laboratory conditions
Acroloxus coloradensis shows significantly less activity and lower fecundity
than Ferrissia parallela. The four presently known eastern localities for A.
coloradensis are all near the northern edge of the geographical range of F.
parallela, and the two species were collected together at only one of these
localities. Direct competition between the two species may therefore occur
only in a minority of localities where Acroloxus now lives.

10

Zoogeography

The Recent distribution of A. coloradensis in North America, i.e., with
populations in the Rocky Mountains from Colorado to Alberta and in north-
central Quebec (and probably in northeastern Ontario), is indicative of a
much wider geographical range in previous time. The early Pleistocene records
in Kansas and Nebraska support this. The similarities between A. coloradensis
and A. lacustris imply that the two species are closely related. There is no
direct evidence available to indicate whether or not Acroloxus utilized the
Pleistocene Beringian land bridge.

It is quite possible that A. coloradensis is even now more widely
distributed in North America than the Recent records indicate. As reported
by Henderson (in Basch 1963: 413), by Russell and Brunson (1967: 33),
and in some detail by the present study, it occupies a seemingly inhospitable
habitat and one which is not searched thoroughly by most collectors. In the
Quebec localities visited, adults that had overwintered also occurred in low
densities, i.e., about one individual in 5 sq. metres of substrate. It appears
probable that this primitive species may be adapted to survive in specialized
habitats where predator pressures are low and competition from more advanced
limpets and other molluscs is less intense.

The relationship of empty unionid shells and of algae that concentrate
calcium carbonate in providing shell-building material for limpets, especially
in soft-water habitats, needs to be investigated. For example, in a thoughtful
paper Russell-Hunter et al. (1967) have shown that a population of Ferrissia
rivularis in Black Creek, New York, has a higher concentration of calcium
carbonate in its shells than some other populations studied. This seemed
anomalous because Black Creek water has the lowest concentration of dis-
solved calcium carbonate of the seven F. rivularis habitats examined. This
lack of correlation was presumed to be indicative of physiological races in
F. rivularis. Black Creek has (or had, in 1957) a dense population of the
soft-water but long-lived mussel Margaritifera margaritifera (Clarke and Berg
1959: 18), however, and the abundant shells of that species might well have
been an important supplementary source of calcium carbonate for the limpets.

11

Addenda

While this paper was in press, three additional adult specimens of
Acroloxus coloradensis (two collected alive) were received from Dr. John
G. Oughton, Department of Zoology, Ontario Agricultural College, University
of Guelph, Guelph, Ontario. These were collected by Dr. Oughton and
Mr. D. G. S. Wright on September 1, 1967, from a small pond 1172 miles
north of the village of Arkell, Nassagawaya Township, Halton County,
Ontario. This find considerably extends the known range of A. coloradensis.

Dr. Oughton’s field notes state that the pond basin is five to ten acres
in area but that encroachment by Typha has reduced open water to about
75 x 100 feet. The pond bottom is mud and plant detritus, and the pond is
heavily vegetated. Yellow water lily is dominant, and Riccia, Lemma, Carex,
and Nympha were also noted. Other molluscs found during a half-hour
search by both men are Lymnaea stagnalis (not common); Helisoma trivolvis
(few); Lymnaea elodes (very few); sparse empty and immature shells of
Physa, Planorbula, and Gyraulus; three specimens of Sphaerium; and one
of Pisidium.

I am grateful to Dr. Oughton for permission to include this information,
and to Dr. Jorgen Knudsen, Zoological Museum, Copenhagen for generously
providing specimens of Acroloxus lacustris for comparison.

Literature Cited

BASCH, P. F.
(1963). A review of the Recent freshwater
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the Museum of Comparative Zoology 729
(8): 401-461.

BONDESEN, P.
(1950). A comparative morphological-
biological analysis of the egg capsuls of
freshwater pulmonate Gastropods. Natura
Jutlandica 3: 1-208, pl. 1-9.

BURCH, J. B.
(1962). Cytotaxonomic studies of fresh-
water limpets (Gastropoda: Basomma-

tophora). 1. The European Lake Limpet,
Acroloxus lacustris. Malacologia /(1):
55-72.

CLARKE, A. H., AND C. O. BERG
(1959). The freshwater mussels of central
New York. Cornell University, Memoir
367: 1-79.

HENDERSON, J.
(1939). Ancylus coloradensis, new name for
A, hendersoni Walker, 1925, not 1908. The
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HUBENDICK, B.
(1962). Studies on Acroloxus (Moll. Ba-
somm.). Meddelanden Fran Goteborgs
Musei, Zoologiska Avdelning. 133: 1-68.

RUSSELL, R. H., AND R. B. BRUNSON
(1967). Acroloxus coloradensis from Mon-
tana. The Nautilus 87 (1): 33.

RUSSELL—HUNTER, W., M. L. APLEY, A. J. BURKY,
AND R. T. MEADOWS
(1967). Interpopulation variations in cal-
cium metabolism in the stream limpet,
Ferrissia rivularis (Say). Science 155 (3760):
338-40.

TAYLOR, D. W.
(1960). Late Cenozoic molluscan faunas
from the High Plains. (United States)
Geological Survey Professional Paper 337:
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WALKER, B.
(1925). New species of North American
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15

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