Life Sciences Contribution 81
Royal Ontario Museum
The Ejaculatory Complex
in Water Mites
(Acari: Parasitengona):
Morphology and Potential
Value for Systematics
David Barr
RO M
DIRE SICKENCES CONTRIB UPIONS
ROYAL, ONTARIO MUSEU M
NUMBER 81
DAvIDBARR Lhe Ejaculatory Complex
in Water Mites
(Acari: Parasitengona):
Morphology and Potential
Value for Systematics
Publication date: 30 October, 1972
Suggested citation: Life Sci. Contr., R. Ont. Mus.
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Contents
Abstract, /
Résumé, 2
Introduction, 3
Objectives, 3
History of Water Mite Classification, 3
The Genus as Operational Unit, 5
The Ejaculatory Complex, 5
Problems in Mite Taxonomy, 6
Methods, 7
Functional Morphology of the Ejaculatory Complex in Hydrodroma, 8
Historical Introduction, &
Male Reproductive System, 9
Chitinous Skeleton of the Ejaculatory Complex, /2
Musculature, 17
Functional Interpretation, /7
Discussion, 22
Survey of the Ejaculatory Complex in Water Mites, 23
Historical Introduction, 23
Male Genital System in Terrestrial Mites, 23
Comparative Studies in Water Mites, 23
Descriptions: Species Ordered Alphabetically, 24
Albia
Arrenurus
Atractides
Aturus
A xonopsis
Brachypoda
Eylais
Feltria
Forelia
Frontipoda
Geayia
Hydrachna
Hydrovolzia
Hydryphantes
Hygrobates
Koenikea
Kongsbergia
Lebertia
Limnesia
Limnochares
Midea
Mideopsis
Neumania
Oxus
Piona
Protzia
Pseudohydryphantes
Sperchon
Sperchonopsis
Testudacarus
Thyas
Tiphys
Torrenticola
Tyrrellia
Unionicola
Assessment and Analysis of Similarities, 64
Homology, 64
The Generalized Water Mite EC, 64
Similarity Groupings, 65
Discussion, 7/
Basic Conclusions, 7/
Importance For Classification, 72
Phylogenetic Significance, 72
Summary, 74
Glossary of Morphological Terms, 75
Acknowledgments, 75
Literature Cited, 79
Appendix A: Traditional Classification of Water Mites (adapted from
Viets and Viets, 1960), 84
Appendix B: Johnston’s Classification (1965) of Water Mites
(adapted), 84
Appendix C: Data for Collections Examined, 85
The Ejaculatory Complex
in Water Mites
(Acari: Parasitengona):
Morphology and Potential
Value for Systematics
Abstract
The water mite ejaculatory complex was investigated to
provide new systematic information. As a basis for com-
parison, a functional morphological study was first completed
for the ejaculatory complex (EC) of Hydrodroma sp. (nr.
H. despiciens). Cleared skeletal mounts, serial sections, and
other preparations were used to elucidate structure. Finally
EC structure was compared for 45 species of water mites
classified in 36 genera and 24 families. The most useful
technique involved preparation of cleared skeletal mounts
and observation by interference contrast (Nomarski phase)
microscopy.
The EC of Hydrodroma is shown to be an elaborate,
muscled, chitinous syringe-mechanism for the ejection of
a mass of spermatozoa as a spermatophore. Structure is
described and a working terminology established. A detailed
functional hypothesis (based on morphology and general
behaviour) is developed, and indications of the value of the
EC character complex for systematic work are noted. The
basic EC structure for all species studies (except Hydro-
volzia sp.) is homologous with that of Hydrodroma. General
EC function also appears to be similar throughout, although
differences in detailed mechanism are suggested by varia-
tions in skeletal structure. Using the EC as an indicator
of relationship, several informal suprageneric groupings,
coinciding only partially with conventional classifications, are
delimited.
A primary conclusion is that evidence from the EC is
consistent with a hypothesis of monophyly for the water
mites.
Résumé
On a examiné le complexe éjaculatoire des mites aquatiques
a la recherche de nouvelle information systématique. Com-
me fondement d’une étude comparative, d’abord une inves-
tigation de morphologie fonctionelle a été complétée pour le
complexe é€jaculatoire (abrégé EC) de Hydrodroma sp. (prés
de H. despiciens). Des préparations squelettiques claires,
sections sériales, et des autres préparations ont été utilisés
pour élucider la structure. C’est suivi par une évaluation
comparative de la structure de ?TEC pour 45 espeéces de
mites aquatiques classifi¢es en 36 genres at 24 familles. La
méthode la plus convenable utilise les préparations claires du
squelette chitineux et l’observation par microscopie d’inter-
férence contrastée (Nomarski phase).
L’EC de Hydrodroma se montre comme un mécanisme de
seringue élaboré, musculeux, chitineux, pour léjaculation
d’une masse de spermatozoa en une spermatophore. La
structure est décrite et une terminologie faisable est établie.
Une hypothése fonctionelle détaillée (fondée sur la morpho-
logie et sur le comportement général) est dévelopée, et des
indications sont notées donnant le valeur de la complexe de
characteres pour le travail systématique. La structure fon-
damentale de l’7EC pour toutes les autres espéces de mites
aquatiques étudiées (avec l’exception de Hydrovolzia sp.)
est homologeuse a cela de Hydrodroma. La fonction géné-
rale, elle aussi apparait d’étre pareille pour toutes les espéces,
bien que des variations en mécanisme détaillé soient sug-
gérées par des variations en structure squelettique. En
employant ’EC comme indicateur de relations, plusieurs
catégoires supra-génériques informales sont délimitées, et
celles-ci ne sont que partiellement d’accord avec les classi-
fications conventionelles.
Une premicre conclusion est que lévidence de TEC
conforme a une hypothése de monophylie pour les mites
aquatiques.
Introduction
Objectives
An objective classification of animals based on a broad _ biological
characterization rather than the narrow basis of descriptive external
morphology is essential if classification is to serve as an information
storage system with high predictive value. The need for this sort of
approach at the supra-generic level is strikingly apparent in water
mites. Mitchell (1964b) termed the family groupings arbitrary and
inconsistent and, in proposing a solution to this undesirable situation,
discussed studies in functional morphology, chromosome structure, larval
morphology, and larval behaviour. He concluded that the most stable
higher classification would be derived from a synthesis of a series of
similar, independent investigations of biological systems.
Mitchell (1957a, 1958a) also indicated that characters other than those
of the external plates of the body wall may form the only reliable basis
for suprageneric classification in mites. His view arises from the probable
assumption that small-bodied forms such as mites, with an unspecialized
mode of locomotion, have little functional need for exoskeletal sclerites
and may have undergone extensive evolutionary radiation while remaining
in the “soft-bodied” condition.
Several modern comparative studies (Bader, 1954, 1969; Sokolow,
1954; Mitchell, 1957a, 1962; and Sparing, 1959) of biological systems
in water mites are now available, but more are needed before a stable and
practical family classification can be derived. The same data are required
for more realistic and complete estimates of water mite phylogeny.
Thus, the primary aim of the present study was to make available for
systematic purposes a body of comparative data on one functional system
within the water mites and to integrate this new material as another
information module in our available knowledge. At the same time it
has been possible to increase our understanding of the reproductive bio-
logy of aquatic Parasitengona and to elucidate the structure of an organ
that will prove useful at all levels of taxonomy, in particular, that of
specific discrimination and identification.
History of Water Mite Classification
Thor (1903) summarized some of the classification schemes used for
mites before 1900, in most of which the true water mites were grouped
in the single family Hydrachnidae. This family was gradually divided
into subfamilies by Piersig and Lohman (1901), Koenike (1909), and
K. Viets (1916). Eventually, Hydrachnidae was much restricted, and
numbers of new families were erected (see Thor, 1903; K. Viets, 1929,
1936; Lundblad, 1941b).
The most widely accepted classification is perhaps best exemplified in
that employed by Viets and Viets (1960, see Appendix A). It consists
(for central European species) of 31 families, 16 of which are monotypic.
The families are grouped into 11 superfamilies, and are arranged in
3
natural (evolutionary) order, the most primitive families listed first and
the most advanced (derivative) last. This classification is based almost
entirely on the external exoskeletal morphology of adult mites, particularly
structures of the palp, genital plates, coxae, and legs, and it has been
constructed by many workers over the past 70 years largely on the basis
of intuition and tradition. Thus it is difficult to find an explicit statement
in the literature as to why, for instance, the Torrenticolidae are more
similar structurally to the Lebertiidae than to the Sperchonidae.
Grandjean (1935) discovered that all mites could be separated into
two groups by the presence or absence of actinochitin (optically active
chitin) in the core of simple setae. This and other correlated characters
were incorporated into recent classifications of the Acari by Evans et al.
(1961) and by Johnston (1965). Most recent authors agree that the water
mites are Prostigmata and should be placed in the group Parasitengona
(variously described as a Cohort, Suborder, etc.) with the closely related
terrestrial families Johnstonianidae, Trombiculidae, Trombidiidae, Eryth-
raeidae, Smaridiidae, and Calyptostomidae, where the larvae differ mar-
kedly from the adults in morphology and habits (usually parasitic larvae
and free-living adults).
Mitchell has devoted much thought to water mite classification and has
repeatedly advanced the idea that the group may be polyphyletic (1954,
1957a, 1962; Imamura and Mitchell, 1967), different groups having
somewhat different affinities within the Parasitengona. Indeed, a number
of recent authors regard the water mites as basically an ecological assem-
blage, with the great diversity of structure and of functional systems a
result of diverse origin. Adult external morphology is so heterogeneous
as to suggest that, in the extreme case, each family could be regarded as
an individual phyletic lineage, independent of all the others. But the work
of Bader (1954) and Mitchell (1957a, 1962) suggests that a smaller
number of broad phyletic lines would best explain the situation. Johnston
(1965) was apparently influenced, in part, by Mitchell’s findings in the
preparation of his catalogue of mites (see Appendix B).
Johnston included all water mites in 10 superfamilies, each equal in
rank with those of the terrestrial mites also in the Parasitengona. The
last seven superfamilies are informally grouped as the Hydrachnellae
(s. str.), resulting in four main groups within the water mites; viz,
Hydrovolzioidea, Eylaoidea, Hydryphantoidea, and Hydrachnellae (s. str.).
The implication is that the four main groups of water mites are no more
closely related among themselves than they are to any of the superfamilies
of terrestrial mites. Krantz (1970) used a similar classification.
Except for the above-mentioned studies, a conscious and objective in-
vestigation of the problem of grouping genera into families has not been
attempted. The genera are so distinctive that they form the units by
which most students learn to recognize different types of water mites,
and the most workable keys are to genera only (Newell, 1959). Keys to
the families and family diagnoses (Baker and Wharton, 1952: 259-319)
are so complex, full of exceptions, and difficult to grasp intuitively that the
validity and objectivity of most of the presently accepted family groupings
is doubtful.
4
The Genus as Operational Unit
As indicated above, the genus appears to be the most stable supraspecific
taxon in water mites and is the most readily defined unit of diversity and
evolutionary radiation. Few genera, once erected, have required further
modification, and although the taxonomic level of a generic grouping of
species may be changed, it has seldom been necessary to thoroughly dis-
sociate the members of such a grouping in spite of the description of
thousands of new species from all parts of the world since 1900. The
corollary is that there are few, if any, “dumping ground” genera com-
posed of a heterogeneous assemblage of species. As a further corollary,
within the water mites, interspecific variation within generic bounds is
almost invariably smaller than interspecific variation across generic
lines. Consequently, the present study was based upon a comparison of
genera as represented by one or a few available species.
This is the so-called exemplar method of comparative biology (Sokal
and Sneath, 1963: 161), and its justification is based upon the observation
that when it is not possible (for reasons of time, labour, poor collections,
etc.) to base observations on large samples of the units of a given taxon,
reasonably dependable results can be obtained by using representative
units. The success of this method depends upon the probability that a
randomly chosen taxonomic unit will be typical for the taxon it represents,
a probability that is much increased when the taxa are as homogeneous as
water mite genera. The method has been tested. several times with
favourable results (Sokal and Sneath, 1963: 162; Moss, 1968).
The Ejaculatory Complex
Throughout all groups of the Arthropoda, wherever genitalia or intro-
mittent organs of complex form are found, the comparative morphology
of these structures has provided a rich source of data for use in species
definition, classification, and phylogenetic speculation at all taxonomic
levels. This is true in such widely different groups as Anostraca (Dexter,
1959), Astacidae (Hobbs, 1942a, 1942b), Diplopoda (Keeton, 1960),
Araneida (Comstock, 1948: 106-121) and Acarina (Feider, 1959), as well
as for almost every order of Insecta (Tuxen, 1956). But until the present,
the use of this fund of information for the elucidation of systematic pro-
blems in the water mites has been limited. Although the aquatic Parasi-
tengona have been intensively studied for at least 100 years and constitute
perhaps one of the best understood subunits of the Acari, and although the
generic classification has reached a mature and stable level, the simple
descriptive morphology of the chitinous male organ, known as_ the
penisgeriist Or ejaculatory complex, has so far been neglected.
The ejaculatory complex has been referred to in different ways by
various authors. Perhaps the term most commonly applied to it is Penis,
but it is inappropriate to continue this usage as penis commonly refers to
a flexible membranous or muscular intromittent organ in other invertebrate
and vertebrate groups. Phallus is unsatisfactory also, for it implies merely
a
an intromittent organ, a through passage for sperm transfer. The ejacula-
tory complex of water mites, however, is not always used for intromission
and usually serves other functions in addition to simple sperm transfer.
Aedeagus can be applied only to the sclerotized distal section of the
phallus in insects, often litthe more than a sclerotized tube. Authors
writing in German have generally applied the term penisgeriist to the
organ, literally ““(supporting) framework of the penis.” This term is cor-
rect in a narrow sense if the walls of the sperm passage are considered
to represent a membranous penis, but its use seems to deny the probable
ontogenetic origin of the sclerites from the walls of the passage and
completely neglects the functional character of the organ in spermatophore
formation. Thus, in every way, the name ejaculatory complex as defined
by Mitchell (1964a) in his study of the trombiculid, Blankaartia acuscu-
tellaris, describes best the muscled, chitinous framework that participates
in formation of a spermatophore as well as ejection and deposition of the
spermatophore outside the body of the male. This term will often be
abbreviated to EC in the present report.
Problems in Mite Taxonomy
Although the limits and diagnostic characters for most genera of water
mites are well understood, the species-level taxonomy, especially of non-
European forms, is unsatisfactory. Of the approximately 75 genera known
from North America, only about 15 have been revised since 1950, and
keys are available for only a few of these. The other 60+ genera are
known only from scattered and inadequate species descriptions and a few
dated monographs by Wolcott (see references in Crowell, 1961). A major
revisionary effort is needed before even the adults of most North American
species can be determined with confidence (for example, see Paterson,
1970).
The unsatisfactory taxonomic situation has proven a difficulty in the
present study, and the following conventions were followed in discussing
the water mite species examined. Each species was represented by indivi-
duals from a monospecific population (judged on morphological criteria)
from a single locality (collection data in Appendix C). Thus, the unit of
study was not a species but a representative (and relatively uniform) sub-
population (or deme) of that species. This practice will tend to insure that
characters of more than one closely related species will not be confused.
Species names are applied to such populations only where the identifica-
tion seems unequivocal, and in each such case I have cited the source upon
which the determination was based. The designation near (nr.) indicates
that there are good reasons to believe that the mites examined are mem-
bers of this species, but that revisionary work and/or reference to types
is required before a precise determination can be made.
Methods
Cleared skeletal preparations of the EC were studied by light micros-
copy, both bright-field and interference contrast (Nomarski phase). Most
of the structural detail is illustrated in paired anterior and lateral views.
All illustrations are semi-diagrammatic in that sclerites are delimited
somewhat more clearly than they appear in the preparation, while small
changes were sometimes necessary to clarify structure or position. Each
drawing is oriented with the distal end of the ejaculatory complex pointing
towards the bottom of the page. Thus the lateral view is of the left hand
side. The scale accompanying each pair of figures represents a length of
50 », and a single scale serves for both illustrations of each species.
Specimens for gross dissection and serial sectioning were prepared by
the cellulose nitrate infiltration procedure described by Mitchell (1964a).
Serial sections were stained with Mallory’s triple stain (Gray 1964: 111).
Each species population examined is represented by a small series of
voucher specimens deposited in the collection of the Department of Ento-
mology and Invertebrate Zoology of the Royal Ontario Museum, Toronto,
Ontario.
Abbreviations used in the figures and descriptive portions of the text
are listed below.
AMScl: anterior margin sclerite. DisRm: distal ramus.
AntHn: anterior horn. Dissc: /) distalesclemte,
AntK]: anterior keel. DLBd: distolateral border.
AntRm: anterior ramus. EC: ejaculatory complex.
Apcl: apical development. LtrSf: lateral shelf.
ApRm: apical ramus. LWScl: lateral wall sclerite.
ApSt: = apical seta. PosKl: _ posterior keel.
BsPI: basal plate. PrxAm: proximal arm.
Cmb: chamber. PrxCmb: proximal chamber.
CmbRm: chamber ramus. PrxHn: proximal horn.
DisAm: distal arm. PrxSc: proximal sclerite.
DisRd: distal rod. PstRm: posterior ramus.
Functional Morphology of the
Ejaculatory Complex in Hydrodroma
Historical Introduction
Early workers investigated the male reproductive system of water mites
in some detail. Koenike (1888), von Schaub (1888), Michael (1895),
Pollock (1898), Nordenskiold (1899), Thon (1900), Thor (1903),
Lundblad (1930), and Schmidt (1935) considered some aspects of the
sclerotized penisgeriist, but none succeeded in producing a meaningful,
three-dimensional explanation of the structure. Thus, no adequate func-
tional hypothesis was developed. Because Schmidt, the most thorough of
these investigators, worked primarily with Hydrodroma (=Diplodontus)
despiciens, this species was chosen for intensive investigation.
Additional evidence on the EC may be available in Croneberg (1878)
or in Musselius (1912; cited by Mitchell, 1955). Neither publication
could be obtained for the present study. |
Purely taxonomic studies have made little use of the ejaculatory com-
plex (see Koenike, 1901; 1902; Lundblad, 1941a, 1943; 1956;[K70:
Viets, 1965, 1968). Usually, only a semi-detailed drawing has been
offered with one or two prominent features noted in the text. There is no
standard structural terminology.
Mitchell’s morpohological publications on Unionicola and Najadicola
(1955), Thermacarus and other thermophiles (1960), water mite mouth-
parts (1962), and Limnochares and Eylais (1964b) did not treat the
EC, but demonstrated a variety of little-used techniques that proved
valuable in the present study.
I sought basically to repeat Schmidt’s work, with the addition of gross
dissection and skeletal preparation techniques to more thoroughly explore
the three-dimensional structure of the ejaculatory complex and to discover
its functional significance. Schmidt’s (1935) observations on the soft
parts of the genital system were accurate and are, in part, repeated here
by way of summary and orientation.
The species studied has long been known as Hydrodroma despiciens
Miller. It is common, shows little variation over its broad range in North
America, and appears to be the same as the European species of that
name. The assumption that North American mite populations belong to
European species on the basis of adult morphology alone is, however,
unwise. Several of these associations have been proven incorrect in the
past. A thorough comparison of North American and European popula-
tions of H. despiciens might also show specific differences.
The Hydrodroma collected from Lake Myosotis, Rensselaerville, N.Y.,
are uniform in the structure of the ejaculatory complex. This population
also is similar to samples examined from other collections in northeastern
North America.
Male Reproductive System
The testes, multilobed and filling much of the body cavity, surround the
gut and push anteriorly, crowding the salivary glands. Each lobule empties
via a sperm duct that unites with others in a branching system leading
ultimately to a pair of long, wide, seminal vesicles lying midway (dorso-
ventrally and anteroposteriorly, Fig. 1c) in the body. These seminal vesi-
cles are anteroposteriorly elongate and lie one on either side of the midline,
with the products of the testes entering dorsoposteriorly. Exiting antero-
ventrally from each seminal vesicle is a narrow, tubular, muscular-walled
vas deferens that travels anteroventrad in the direction of the genital
opening. After a short distance (Figs. lc, 5a) the vasa deferentia turn
posteromediad and unite to form a wide, thin-walled, muscular tube, the
ductus ejaculatorius. The ductus proceeds posterad for a short distance
and narrows, bending ventrally at the same time and entering the ejacu-
latory complex.
The ejaculatory complex lies in the median plane and is usually posi-
tioned with its longitudinal axis in an oblique anteroventral to postero-
dorsal direction, the free distal end pointing toward the genital opening
(Fig. la). For clarity and ease of usage, all subsequent terminology
associated with this organ will be based on the assumption that it is
oriented directly dorsoventrally, the distal end being ventral and the
proximal end dorsal. Thus, the cephalic-facing and caudal-facing surfaces
will be termed simply anterior and posterior, respectively. The organ lies
at the distal end of the ejaculatory duct and just inside the genital opening
in the body wall. Lightly sclerotized distal membranes join its apex to
the margins of the genital opening so that the extreme distal tip is an
external structure concealed in a phallocrypt (Fig. 1b). The structure is
apparently maintained in place in the body cavity by a network of thin,
cross-banded fibers inserted generally over its surface (particularly on
membranous areas), and having their origin on the inside of the genital
plates, on the distal membranes, on the endosternite, and on denser tracts
of such fibers lying in the body cavity. Schmidt (1935) interpreted these
fibers to be muscular, but Mallory’s triple stain (Gray 1964:111) pre-
parations would indicate that they are chitinous endocuticular fibrils of
the same nature as those forming muscle tendons. The endosternite is a
short, transverse tract of endocuticular material lying anterior to the
ejaculatory complex and serving as the point of origin for a number of
important body muscles.
The external genitalia of male Hydrodroma consist of two ovoid plates
that are somewhat pointed anteriorly and posteriorly and lie on either side
of the elongate genital opening. Each bears approximately 60 (+ 10)
genital acetabula and, on the concave medial border, a narrow tract of
setae. Convincing evidence that the acetabula are sensory organs was
advanced by Thor (1903) and by Schmidt (1935).
EC
excretory pore
coxa
E accessory gland
( \
EC
genital plate
gnathosoma
: ~_ phallocrypt
Ib
seminal vesicle
i ore
genital plate excretory Pp
Fig. 1 Hydrodroma anatomy: a, three-dimensional diagram to indicate the position
of the ejaculatory complex; b, diagrammatic cross-section illustrating the
relationship of the EC to the ventral body wall; c, diagrammatic sagittal
section of a male showing the relationship of the EC to the rest of the
male reproductive system.
10
DisAm
AntRm
DisRm
Sa
ea DisSc 1
4
ie DisSc 2
Ze
Fig. 2 EC skeleton of Hydrodroma: a, anterior view; b, lateral view; c, partial
posterior view; d, perspective view.
ded
Chitinous Skeleton of the Ejaculatory Complex
The ejaculatory complex is typically a two-layered, chitinous structure of
the same basic cuticular composition as those of the exoskeleton. It is
probably produced by evagination and subsequent sclerotization of the
internal wall of the distal portion of the ductus ejaculatorius, which is
embryologically an invagination of the ectoderm. This interpretation is
supported by the observation that even the heavily sclerotized arms of
the ejaculatory complex show a circular pattern of cuticular structure
(Fig. 4a) as though originating as tubular evaginations of the ductus.
Because of the method of its formation, the analysis of EC structure
in terms of well-defined sclerites is difficult. Heavily sclerotized and
apparently distinct areas often grade imperceptably into lightly sclerotized
or membranous areas. The articulation between sclerites may not be a
definite suture or joint but an imperfectly defined membranous area that
is continuous with both sclerotized structures. Thus, for the purpose of
this study, sclerites were delimited somewhat arbitrarily so that they could
be referred to as structural landmarks. Points of muscle attachment are
usually recognizable because the sclerites are roughened and pitted to
increase the surface area for bonding in a manner similar to that observed
for muscle insertion on vertebrate bones.
New terms have been defined throughout this study for structures of
the EC skeleton. The names proposed are derived from English and are
descriptive of position and general shape. All such terms appear in bold-
face where they first occur in the text and are redefined in the glossary,
p. 75. Abbreviations used in the figures are shown with first usage of
the term, in the glossary, and in a complete list, p. 7.
No attempt was made to homologize parts of the ejaculatory complex
of this species with the sclerites described by Feider (1959) for the
Trombidioidea although there is undoubtedly an evolutionary relationship.
Until the relation of Feider’s sclerites to the soft parts is better known,
functional and structural homologies will be difficult to interpret. Needed
are more investigations of the type done by Mitchell (1964a) for the
trombiculid, Blankaartia.
The main supporting framework of the EC (Figs. 2, 3) consists of
two pairs of sclerites, the paired proximal arm sclerites and paired distal
arm sclerites. The ductus ejaculatorius proper empties into an enlarged
proximal chamber (PrxCmb), which is roughly cubical, with lateral, proxi-
mal, and posterior walls sclerotized. The anterior wall is largely membra-
nous and is the point of entry of the ductus. The lateral walls approach
each other distally, and the chamber is narrowed and open on the distal
side. The lateral walls are strengthened along their anterior and distal edges
by the more heavily sclerotized anterior margin sclerite (AMScl). The
anteroproximal edge of the chamber is especially heavy and bears a pair
of proximal horns (PrxHn). The anterior third of the proximal wall is
also heavily sclerotized, and a lateral wall sclerite (LWScl) travels dia-
gonally across each lateral wall providing additional rigidity. The thick-
ened sclerites of the distolateral borders of the chamber run posteriorly and
join with the proximal arm sclerites.
Zz
After entering the anterior side of the proximal chamber, the sperm
passage proceeds distally to the exterior. Lying on either side of the
sperm passage are the main supporting elements of the EC, the paired
proximal and distal arm sclerites. Each proximal arm sclerite consists
of four rami. The largest is the thick, curved proximal arm (PrxAm) that
projects proximolaterad from the body of the EC, then curves mediad to
partially encircle the proximal chamber. The tips and lateral margins of
this arm are roughened and pitted to facilitate muscle insertion. A distal
ramus (DisRm) proceeds distally along the posterior wall of the EC, the
distal rami of either side lying close together on either side of the midline.
A medial ramus projects toward the midline of the EC and appears to
articulate with its fellow from the opposite side. This articulation is the
sole point of direct contact between the two proximal arm sclerites. A
short chamber ramus (CmbRm) has its origin at the point where the
proximal arm contacts the lateral wall of the proximal chamber. It travels
proximad for a short distance in the lateral wall and articulates with the
distal end of the lateral wall sclerite.
The posterior wall of the proximal chamber is moderately sclerotized
and grades distally into the lightly sclerotized areas surrounding the distal
rami of the proximal arm sclerites in the posterior wall of the midsection
of the EC. This latter wall is strengthened in addition by three pairs of
submedian distal sclerites (DisSc) (Fig. 2c) that appear to articulate with
the distal rami. The members of each pair are proximodistally elongate
and lie side by side in the posterior wall of the distal half of the EC. The
proximal pair are short and thin, the middle pair short and thick, whereas
the apical pair are long and taper distally to attenuate apices. The apical
distal sclerites extend beyond the apex of the EC, and the attenuate
tips project into the phallocrypt. The proximal distal sclerites appear
to articulate proximally with the point of articulation of the medial rami
(within the body of the EC). The articulation with the distal rami occurs
in the posterior wall at the point at which middle and apical sclerites are
in contact.
A laterally compressed evagination from the posterior wall of the
proximal chamber forms a thin posterior keel (PosKl). The lateral walls
of this structure and the posterior walls of the chamber are thickened
at the point of contact, and the chamber cavity projects a short way into
the keel. The keel is expanded into a flattened kidney-shape, and its
surface is pitted and sculptured to facilitate muscle attachment. The keel
bears a distal rod (DisRd) projecting distally and curving anteriorly so
that it eventually lies adjacent to the posterior wall of the distal end of
the EC and terminates in the distal membranes. This rod is lightly
sclerotized (almost membranous) in Hydrodroma.
Each of the paired distal arm sclerites bears three main rami. The
distal arm, projecting laterally from the EC at an angle of approximately
50° to the longitudinal axis, is strong, cylindrical, and relatively straight to
the tip, where there is a gradual curve proximad. The tip of each arm
is flattened and bears medial horizontal flanges that are sculptured for
muscle attachment. The anterior ramus (AntRm) projects distally and
is
Fig. 3 Photomicrographs of the EC skeleton of Hydrodroma, overall length
220 ,: a, anterior view, optical section in plane of proximal and distal
arms, interference contrast; b, lateral view, optical section in median
plane interference contrast; c, anterior view, scanning electron micro-
graph; d, three-quarter view (disto-antero-lateral), scanning electron
micrograph.
anteriorly, arching over the EC and fusing, on the midline, with the tip
of the same ramus from the opposite side. On the distal border of this
ramus, there is no clear line of demarcation between the heavily sclerotized
ramus and the sheet of gradually less sclerotized membrane that leads
14
externally to the margins of the genital opening. The posterior rami
(PosRm) of the distal arm sclerite lie along the lateral margins of the
posterior wall of the midsection of the EC and each is fused with an
elongate sclerite lying in the same plane but slightly mediad. These
paired posterolateral sclerites are attentuate distally (not projecting beyond
the distal arm sclerites) and heavier posteriorly where they broaden and
expand considerably to fuse with the distal, lateral, and posterior walls
of the lateral chambers (Cmb 1).
On either side, the distal arm is attached to the posterior wall of the
EC (and to the posterior rami) by a thin, sclerotized lateral shelf (LtrSf).
The shelf fills the triangular axillary area between the distal arm and the
posterior ramus and proceeds proximad to fuse with the posterior wall of
the lateral chamber. The proximal margin of this shelf is irregular but
roughly concave.
The anterior wall of the EC distal to the proximal chamber is covered
by two anterior sclerotized surfaces that slope from the midline on the
anterior surface posterad to the lateral shelf on either side. Proximally
these surfaces expand to form part of the distal and anterior walls of the
lateral chambers. Distally they narrow and proceed under the arch
formed by the anterior rami of the distal arm sclerites, at the same time
tapering, becoming less heavily sclerotized, and eventually uniting with
the membranes delimiting the phallocrypt. Where the anterior sclerotized
surfaces meet along the midline, they fuse and are expanded anteriorly
to form a high, broad, thin, strongly sclerotized anterior keel (AntK]).
Each of the sclerotized surfaces is strengthened by a thickened area lying
along the base of the keel and extending part way up its distal edge.
The keel is strongly sculptured and pitted for muscle attachment.
The area from the base of the proximal end of the anterior keel to the
anterodistal border of the proximal chamber is membranous and conti-
nuous with the membranes of the anterior wall of the proximal chamber.
The membranes of this area are supported by one pair of rod-like proxi-
mal sclerites (PrxSc 1). These sclerites extend obliquely from the anterior
side of the lateral chambers, proximomediad to the anterior end of the
distolateral border of the proximal chamber.
The sperm passage (Figs. 1c, 5a) enters the proximal chamber through
the anterior side, expands, and narrows as it leaves the chamber dis-
tally. The shape of this passage in the distal part of the EC is elaborate
(Fig. 4) with extensions into the lateral chambers, but the general course is
distad, exiting between the distal apices of the distal arm sclerites. Schmidt
(1935) described a series of setae along the sperm canal that were not
observed here.
The distal membranous cone leading to the margins of the genital
opening and forming the walls of the phallocrypt is attached to the
ejaculatory complex along the following line: along the distal edge of the
anterior rami of the distal arm sclerite (as previously described), along the
basal half of the distal arm, under the distal arm, proximally along the
lateral shelf, and across the entire posterior side of the EC at the level
of the lateral chambers.
Ts
AMScl
PrxAm
AntRm
PrxCmb
ductus ejaculatorius
phallocrypt
Fig. 4 Diagrammatic transverse sections of the Hydrodroma EC skeleton: a, in
the region of the proximal chamber; b, in the region of the distal arm
sclerites; c, in the region of the lateral chambers.
Fig. 5 Musculature of the Hydrodroma EC: a, general view of terminal elements
of male genital tract; b, diagram of the deep muscle groups (4-6); c, dia-
gram of the superficial muscle groups (1-3).
16
Musculature
The musculature of the EC is bilaterally symmetrical, being composed of
six pairs of muscle groups that completely ensheath the sclerotized ele-
ments (Fig. 5). The number of muscle fibers involved in each group, as
in all muscles of this species, is small, not over 10 or 15 at the most, and
only three in the phallic retractors.
The superficial or lateral muscle groups are massive in cross section
(Fig. 5c). The distal dilators (designated muscle group number 1) run
laterally from their origin on the anterior and distal halves of the anterior
keel to an insertion on the medial surface of the distal arm on either side.
The lateral-longitudinal compressors (group 2) are oriented distoproxi-
mally, originating on the posterior and ventral portions of the lateral
surfaces of the anterior keel and on the anterior sclerotized surfaces.
They insert on the anterior and medial surfaces of the proximal arm.
The proximolateral compressors (group 3) are another laterally directed
group, originating on the medial and posterior surfaces of the proximal
arm and inserting on the lateral surfaces of the posterior keel.
The deep or medial muscle groups are illustrated in Fig. 5b. The
mediolongitudinal compressors (group 4) run in a distoproximal direction
from their origin on the apex, proximal edge, and proximal half of the
lateral surfaces of the anterior keel to their insertion on the proximal
horns. The proximomedial compressors (group 5) originate on the proxi-
mal horns and insert on the proximal and anterior edges and proximal part
of the lateral surfaces of the posterior keel. The phallic retractors (group
6), included with the deeper groups for convenience, originate laterally
on the endosternite and insert on the distal arm sclerites near the bases
of the distal arms. All of these muscle groups are of smal! to medium
diameter.
Functional Interpretation
The construction of a hypothesis for the function of the Hydrodroma
ejaculatory complex is based upon three principal kinds of evidence:
the reproductive habits of the species, the form and articulations of the
skeletal components, and the size and disposition of the muscle groups
(plus the similarity to known spermatophore-forming water mites).
Transfer of spermatophores is a common method of fertilization in the
Arthropoda (Snodgrass, 1935: 573; Green, 1961: 69-70; Alexander,
1964; Davey, 1965) and especially in the Acari (Hughes, 1959: 176;
Evans et al., 1961: 23-26). Indeed, it is probably safe to generalize in
stating that, for mites, even where internal insemination takes place, a
spermatophore is still formed and transferred (i.e., the sperm never travel
freely in a fluid medium). Water mites appear to be typical in this respect
(Lundblad, 1929; Mitchell, 1958b; Bottger, 1962, 1965; Efford, 1966).
Whether Hydrodroma practices internal insemination or some form of
spermatophore deposition (both are known for various water mites) is
not yet known, but this point would likely affect only the behavioural
aspects of insemination and not the function of the EC. The motions of
af
spermatophore deposition and internal fertilization should be much the
same, unless perhaps in the latter the EC is extended farther out from the
body (or is more elongate in structure). Therefore I assume that the
functions of the ejaculatory complex in Hydrodroma are to (i) form a
spermatophore, (ii) transport the spermatophore outside the body wall,
and (iil) deposit the spermatophore.
The skeletal components of the EC can be divided into three functional
groups (Figs. 6, 7). The component sclerites of each group are either
fused or bound by tough, inextensible, ligament-like hinges, but the
groups are attached to each other by flexible membrane and have a
limited degree of movement relative to each other. The groups are: (i)
the distal arm sclerites, (11) the anterior keel and anterior sclerotized sur-
faces, and (iii) the proximal arm sclerites and proximal chamber. Groups
(i) and (ii) are joined to each other by short membranous areas that
permit only limited movement. Group (iii), in contrast, is joined to the
other two groups by a wide band of thin, flexible, chitinous membrane that
forms a conspicuous outpocketing on either side at the level of the lateral
chambers. The assumption that each group of sclerites functions as a
unit is difficult to support by movement of prepared specimens, as Eisner
(1957) reported for the ant proventriculus, but is supported by the mode
of deformation and breakage when coverslip pressure is applied.
Muscle groups 1, 2, and 3 are massive, each composed of 10-15 fibres
of large diameter, whereas groups 5 and 4 are smaller because they are
composed of a similar number of smaller fibers. Group 6 is a long, thin
muscle group composed of only three slender fibers. The relative dia-
meter of these groups is probably related to the force applied by each
during EC movements.
The presence of group 6, the phallic retractors, indicates that the entire
ejaculatory complex is probably projected at least part way out of the
genital opening. But there are no muscles attached to the organ that
would be capable of protraction, and so a different mechanism must be
sought. Water mites, in common with a variety of other arthropods
(Manton, 1958; Parry and Brown, 1959; Snodgrass, 1965: 88) utilize
the pressure of the hemocoelic fluid for extension of the limbs (Mitchell
1955, 1957b, 1960), and this same pressure is probably the motive force
pushing the ejaculatory complex out through the genital opening. Thus,
the probable initial events of spermatophore deposition include: (i) con-
traction of the dorsoventral body muscles increasing pressure on the hemo-
coelic fluid, (11) protrusion of the ejaculatory complex to the extent per-
mitted by the distal membranes, and (ili) passive opening of the genital
plates because of the pressure of the EC as it is forced outwards (Mitchell,
1957b):
In this position, the sensory setae inserted on the apices of the distal
arm sclerites in some species (but not Hydrodroma) can be applied to the
substrate to gather tactile information on surface texture, and perhaps help
guide the animal to a suitable site for spermatophore deposition. In speci-
mens preserved in GAW (Koenike’s fluid) (Mitchell and Cook, 1952)
the EC often extends through the genital opening, occasionally lying en-
18
Fig. 6 Postulated action of the distal arm sclerites, transverse section: a, muscle
group 1 relaxed; b, muscle group 1 contracted.
Fig. 7 Postulated action of the sclerite groups of the EC, lateral view: a, all
muscle groups relaxed; i, ii and iii are major sclerite groups; b, contraction
of muscle group 4 rotates proximal chamber counter-clockwise; c, contrac-
tion of muscle group 2 adducts iii up to ii and through i; contraction of
muscle group 1 spreads distal arm sclerites of i (see Fig. 6) and widens
sperm passage; d, simultaneous contraction of muscle groups 5 and 3 vio-
lently compresses proximal chamber and expels the contained mass of
spermatozoa.
19
tirely outside the body. In extreme cases the proximal end is free and
farthest from the body, whereas the distal end is held close to the genital
opening. This type of protrusion of the EC is not natural but is an arti-
ficial situation caused by the extreme osmotic pressures developed during
the process of GAW preservation. When the internal pressure increases
sufficiently, the membranous walls of the phallocrypt are ruptured, and
the EC is forced out. Because the proximal end is held in position only
by the soft tissues of the ejaculatory duct, it is easily displaced. The
distal end is more firmly attached by the tough distal membranes and is
the only part of the EC to remain fixed to the specimen.
A sequence of movements by the ejaculatory complex that results
in spermatophore deposition, once the male has located a suitable site,
can be postulated. Consider the following sequence where the word
“and” indicates simultaneous contraction and the symbol . . . . indicates a
pause inactivity 24,0. 2. t. 43, 25 -andt3. 4-263 Thentthesres-
ponse of the sclerotized skeletal elements could be as follows (Figs. 6, 7):
the proximal chamber is tipped distally, thus aiding in closing the open
side (4); sclerite group (111) slides forward under group (11) and through
group (i) until the widest part of the proximal arm sclerites (at base of
the proximal arm) meets the distal walls of the lateral chambers (2); the
distal arms are pulled medially and anteriorly, articulating with each other
anteromedially and greatly widening the posteromedial area through which
the sperm passage travels (1); the anteroproximal side of the proximal
chamber is pulled distally, further rotating this chamber in a counter-
clockwise direction (4) and bracing it against clockwise torque; the
posterior wall of the proximal chamber is thrust violently anterodistally
by the simultaneous contraction of muscle groups 5 and 3, decreasing the
volume of the chamber and propelling its contents distally and down the
sperm passage. Such a mechanism would effectively expel the semen
components of the spermatophore. The sequence of events described,
however, is only one of several plausible schemes that could be advanced.
Two structural peculiarities present in Hydrodroma and also widespread
in the EC of other water mites show some relevance to the proposed mode
of action. If the proximal chamber is deformed during spermatophore
deposition, then the lateral wall sclerite (Fig. 2b) clearly functions to con-
trol the direction of deformation by maintaining the distance between the
base of the proximal arm and the anteroproximal corner of the chamber
nearly constant on either side. Thus, the primary compression must be
along the anterior-posterior axis. The distal rod (Fig. 2b) appears to be a
second structure well suited to maintaining the distance between parts
of the EC skeleton. Because the rod is membranous in Hydrodroma and
a few other genera, it probably determines the maximum rather than the
minimum distance between its point of origin (posterior keel) and its
point of insertion (posterior surface of EC at level of distal arm sclerites).
The proximal component of the pull exerted by muscle groups 3 and 5
on the posterior keel is thus balanced by the pull of the distal rod in the
distal direction during the simultaneous contraction of these two groups.
This mechanism would leave effective only the anterior component of the
20
force exerted by groups 3 and 5 and so provides a further means of con-
trolling the direction of distortion of the proximal chamber.
The role played by the accessory gland (Fig. 1b, 5a) in spermatophore
formation and deposition is not known. The organ was accurately descri-
bed by Schmidt (1935), and his notes are summarized here. The gland
lies posterior to the EC at the level of the anterior keel and is bipartite, an
elongate, ovoid arm projecting laterally on either side, with each arm
emptying medially into a broad common duct. The common duct opens,
not into the sperm passage, but into the phallocrypt posterior to the
distal tip of the EC. The canals of the two arms are lined with endocu-
ticle which is uniformly perforated. The glandular tissue consists of
columnar cells surrounding each of the arms and presumably discharging
secretions through the perforations into the canals. The point at which
the gland product enters the genital system indicates that it probably is not
used in those aspects of spermatophore formation (e.g., compacting the
sperm mass) that occur within the ejaculatory complex. The secretion
must instead play some role during extrusion of the spermatophore from
the body, perhaps forming a waterproof coating or an attachment stalk
(types 3 and 4 of Brunhuber, 1969). The tubular, sac-like structure of
these glands would make them well suited to the production of a liquid,
proteinaceous coating material of the type described by Davey (1965:
31-33) for the spermatophore of Rhodnius.
In none of the specimens sectioned (collected in September and
October) were products of the testes present in any part of the EC.
Although in most males the lobes and sperm ducts of the testes, the
seminal vesicle, and the proximal sections of the vasa deferentia were
filled with spermatozoa and the carrying fluid (Schmidt, 1935), this ma-
terial did not extend into the EC. In a number of water mites of other
species, however, from which cleared skeletal preparations of the ejacula-
tory complex were made, dense boli of presumably seminal material were
sometimes seen.
The distal parts of the vasa deferentia and the entire ductus ejaculatorius
are provided with a thin circular coat of small muscle fibers that probably
constrict these passages enough to prevent passage of reproductive
products forward beyond the seminal vesicle. Similarly, once the proxi-
mal chamber of the ejaculatory complex has been charged with semen, the
subsequent contraction of the muscle coats would effectively prevent
backward movement of spermatophore materials during the contractions
of the ejaculatory complex muscles responsible for spermatophore depo-
sition. Backflow may be further alleviated by the constriction of the
ductus ejaculatorius caused when muscle group 4 on either side enlarges
during contraction.
As stated earlier, the lateral membranes in the area of the lateral
chambers (Cmb 1) join sclerite group (iii) to the other two groups. It is
possible that upon being charged with semen, the EC expands by separa-
tion of sclerite groups (i) and (ii) from group (iii), with the distention
of the lateral membrane. Consequently a larger portion of the sperm
canal would be filled with semen, but the series of contractions postulated
could still expell the entire mass. Bs
In summary, the ejaculatory complex of Hydrodroma is a syringe-like
organ for the reception, compacting, and expulsion of masses of spermato-
zoa. The proximal chamber is charged with the contents of the seminal
vesicle, and then a series of muscular contractions forces the chamber
distally and compresses it, rapidly decreasing its volume. Simultaneously,
the distal end of the sperm passage is dilated, and the sperm mass is
propelled from the genital tract.
Discussion
Knowledge of the structure of the ejaculatory complex of Hydrodroma sp.
(nr. H. despiciens) provides a useful criterion for investigation. As with
any character complex, this structure may prove to be a sensitive indicator
both of intraspecific, population interactions and of interspecific, taxono-
mic boundaries. H. despiciens has been reported from five continents and
numerous islands (K. Viets, 1956), and it would be surprising if this
widely-applied name has not been used for a number of distinct species.
For example, a specimen from Brazil, determined to be H. despiciens, was
examined during the present study and found to have an ejaculatory com-
plex differing in significant details from that of populations in New York
and Ontario.
A study of the functional aspects of the EC complements morpho-
logical data by broadening the biological significance of the observations
and by permitting the recognition of homologies in other genera. Thus
data are made available for classitication and for phylogenetic speculation.
Unfortunately, although the mode of operation proposed here provides a
groundwork for the study of function in other genera of water mites, the
extensive variations of detailed form and three-dimensional relations of the
component sclerites found in these animals (pp. 24-64) suggest that
many of the details of this hypothesis may be applicable only to Hydro-
droma and closely related genera.
A number of obvious lines of future research are suggested by the
results of the present study. The deduction of ejaculatory complex func-
tion from morphological data should now be checked by a life history
study for the species. Emphasis should be on observation of the method
of insemination and the condition of the reproductive organs at various
times of the year. The ontogeny of the ejaculatory complex in immature
forms should also be studied. Perhaps methods can be developed to fix
specimens in various stages of spermatophore deposition allowing direct
observation of the gross activities of the ejaculatory complex. However,
there seems to be little chance that a way can be found to test the hypo-
thesis of the method of expelling the spermatophore by a syringe-like
contraction. A further possibility is that certain aspects of the operation
of the apparatus in Hydrodroma may be clarified by functional studies in
other genera.
22
Survey of the Ejaculatory Complex
in Water Mites
Histcrical Introduction
MALE GENITAL SYSTEMS IN TERRESTRIAL MITES
There has been considerable comparative and detailed morphological work
on the male reproductive system of mites (summarized by Hughes, 1959).
As noted for water mites (page 8), this research has been concen-
trated on the soft parts of the system to the neglect of the sclerotized
terminal portions (termed the penis by Hughes, op. cit.). Internal sclero-
tized reproductive structures are absent in male Mesostigmata and Metas-
tigmata, and although they are present in both the Oribatei and the Acari-
diae, the distant taxonomic relationship of these groups to the water
mites renders comparisons of little interest. From the standpoint of the
the comparative morphology of water mites, the most important consider-
ation is the structure of the ejaculatory complex in related families of the
Prostigmata, especially the Parasitengona.
Blauvyelt (1945), Hughes (op. cit.::1/6), YThomae (1925), Thor
(1903), Henking (1882), Fredrickson (1961), Moss (1962), and
Feider (1959) reported on the male reproductive system for various
Prostigmata and Parasitengona, but in none do the skeletal elements
resemble the analagous structure in water mites. Mitchell (1964a) studied
thoroughly the enlarged terminal portion of the ductus ejaculatorius in the
trombiculid, Blankaartia acuscutellaris. Although this organ, which Mitchell
termed the ejaculatory complex, is similar in function to the comparable
structure in water mites, little morphological evidence exists upon which
to base a hypothesis of homology. There is no indication, for instance, of
an ontogenetic relationship between the genital sclerites and the walls of
the ductus, as there appears to be in Hydrodroma. Thus, the consensus
of the literature is that no other group of mites possesses a chitinous eja-
culatory complex skeleton of the water mite type.
COMPARATIVE STUDIES IN WATER MITES
Most recent publications pertaining to phylogeny within the water mites
have been cited (Bader, 1954, 1969: Mitchell, 1957a, 1958a, 1962;
Sparing, 1959; Sokolow, 1954). Wooley (1961) reviewed the phylo-
geny of mites and briefly discussed problems within the aquatic taxa. The
early speculation on the phylogeny of this group was based only on exo-
skeletal morphology, a practice that was questioned by Mitchell (1958a).
Nordenskiold (1899) and later authors (Wooley, 1961: 279) variously
concluded that the group was mono-, di-, oligo-, or polyphyletic. Even
then, however, most authorities agreed that water mites evolved from one
or more terrestrial ancestors whose affinities would be with the Prostig-
mata, probably among the Parasitengona.
Bader (1954) studied the comparative morphology of the midgut and
distinguished four main lines of evolution. His scheme represented a con-
siderable simplification from hypotheses based on exoskeletal data, and
23
Mitchell has since shown that other functional and biological systems
may be considered concordant with Bader’s findings; life histories and
larvae (1957a), mouthparts (1962). Recently (1969) Bader extended
his interpretation of midgut structure somewhat and made several tenta-
tive conclusions of the first report more concrete. He recognized explicitly
six distinct subgroups of genera, and suggested specific, separate origins
for five. Sparing, who published (1959) the only comparative study of
water mite larvae to date, concluded from larval morphology that the
water mites (with the exception of Hydrovolzia) constitute a monophyletic
grouping. Mitchell (1958a) also appeared willing in one instance to
postulate a long-surviving, hypothetical water mite ancestor that gave
rise successively to a small number of major evolutionary lines.
Descriptions: Species Ordered Alphabetically
The EC skeleton of the first species for each genus is described fully.
Sclerites of additional species in the same genus are briefly compared to
the first, and major differences are noted.
Albia sp.
(nr. A. caerulea) Fig. 8
Chitinous skeleton of medium size, lightly built; body moderately sclerotized with
walls of midsection largely membranous; arms well developed and strongly sclero-
tized.
PROXIMAL CHAMBER consisting of two main sections, anterior wide, rectangular,
shallow, posterior narrow, elongate, deep, its walls moderately well sclerotized;
anterior margin sclerite wide, not heavily sclerotized; proximal horns borne on an
elongate, sclerotized rod-like proximal ramus, short, blunt, expanded at tips; lateral
wall sclerite narrow, strongly sclerotized, following a sinuate course along lateral
wall of anterior section of chamber from its anteroproximal margin to base of
chamber ramus.
POSTERIOR KEEL reduced, narrow anteroposteriorly, proximal end angular with
margin irregular; distal rod wide proximally, heavily sclerotized throughout its
length, strongly bonded with distal arm sclerites distally.
PROXIMAL ARMS shorter than distal arms, strongly sclerotized throughout,
curved, projecting proximally beyond proximal horns, almost parallel to longitudinal
axis of EC in lateral view; distal rami short, not extending beyond proximal end of
anterior keel; chamber ramus narrow, proceeding anterad then angled proximad,
tapering to a fine point, not articulating apically with any sclerites of proximal
chamber; basal plate not developed.
MIDSECTION of EC with one pair of L-shaped proximal sclerites (PrxScl),
shorter, less heavily sclerotized arm lying proximodistally, its proximal end
continuous with membranous anterior wall of proximal chamber, longer, more
heavily sclerotized arm projecting laterally, ending in a blunt, expanded tip that is
free of the membranes attached to its base; no distal sclerites; large. membranous
lateral chamber (Cmb 1) located in axillary position on either side proximal to
distal arm, walls continuous with distal membranes.
ANTERIOR KEEL low, rounded, surface area reduced, moderately sclerotized,
margins heavily sclerotized, projecting distally beneath distal arch; subtended by a
broadened, moderately sclerotized, U-shaped plate lying in anterior wall of midsection
of EC.
24
Gil
Pil
wyiuy
L 2SX4d
Z 2§X4d
€ 2SX4d
26
isdy
j: i pdy eee : 5 \
Ei ie eae S44] de
\ ON 2 Ayu
wyssd —— Kh } c
q6
L 2SX4d
L>2SX4d
PSM
a, anterior view; b, lateral view.
a, anterior view; b, lateral view.
8 Albia sp. (nr. A. caerulea):
9 Arrenurus crenellatus:
10 Arrenurus intermedius:
Fig.
Fig.
a, anterior view; b, lateral view.
anterior view; 6b, lateral view.
Fig.
a,
Arrenurus lyriger:
Fig. 11
25
DISTAL ARMS long, narrow, strongly sclerotized, projecting proximolaterad at
approximately 30° to longitudinal axis of EC, straight in midportion, curved at
either end; lateral shelf absent; anterior rami forming anterior arch, massive,
heavily sclerotized, not fused anteromedially, broad posteriorly, tapering slightly
anteriorly, then flaring to form an anterior tip that is subtriangular in lateral view;
posterior rami short, heavy, strongly sclerotized, each provided apically with a
medial lobe; distal arm sclerites each with a long, distally tapering, sclerotized,
horn-like apical ramus (ApRm) projecting distad, forming 1/3 of total length of EC
curved (concave anteriorly in lateral view, laterally in anterior view), generally
convergent distally, slightly divergent at tips; no apical setae detected.
Arrenurus crenellatus
Fig. 9
Chitinous skeleton small, compact, only lightly sclerotized; distal and proximal
arms reduced, few strong sclerites. Determined from Cook, 1954a, 1954b, 1955a.
PROXIMAL CHAMBER Oblong in anterior view, deep anteroposteriorly, anterior
side only 1/2 length of posterior, posterior wail strongly convex so that open
anterior side is rotated counter-clockwise through approximately 30° to face
anterodistally; proximal and posterior sides moderately sclerotized, lateral and
anteroproximal walls lightly sclerotized: anterior margin sclerite thickened, mode-
rately sclerotized; no lateral wall sclerite; distolateral border indistinct; proximal
horns absent.
POSTERIOR KEEL elongate in lateral view, tapering gradually into distal rod
which is fused along entire length with posterior surface of EC.
PROXIMAL ARMS reduced, thin, short, not reaching proximally to apex of proxi-
mal chamber; distal ramus and short chamber ramus present; basal plate of two
main sections, one rectangular section proximal to base of proximal arm and
another triangular section distal to base of proximal arm and tapering distally,
strengthened by an oblique, anteroproximal to posterodistal strut fused with base
of proximal arm.
MIDSECTION of EC between proximal chamber and anterior keel largely mem-
branous, supported by a set of proximal sclerites consisting of a pair of elongate,
sinuate lateral rods (PrxSc 1) and a pair of short, anteriorly bifid, club-like, antero-
lateral rods (PrxSc 2); lateral rod of either side (PrxSc 1) incorporated as a
strengthening strut in distal section of basal plate.
ANTERIOR KEEL Of medium size, sclerotized, margin irregular; proximal margin
strengthened by a narrow sclerotized rod that is bifurcate anteriorly and curved
distally along base of keel; keel tapering rapidly distally, narrow end extending
under anterior arch.
DISTAL ARMS greatly modified; rami of distal arm sclerites flattened, expanded
and fused so that sclerites of either side form together a cone-shaped, sclerotized
structure, blunt distally, open posteriorly, encircling distal end of EC; distal arms
recognizable as sclerotized lateral and posterior margins of proximal end of
cone; anterior rami as thickened anterior margin; posterior rami retain a degree
of individuality, forming lateral margins of posterior gap in cone, projecting
proximally beyond cone to level of proximal end of anterior keel, situated far
apart, One on either side of broad posterior surface of EC; lateral shelf also
forms part of lateral and posterior walls of cone; a pair of simple setae situated
subdistally, one on either side of cone.
26
Arrenurus intermedius
Fig. 10
The EC of this species differs from A. crenellatus primarily in being proportionately
narrower and more elongate. Anterior margin sclerite more heavily sclerotized;
distal rod free from body of EC in midsection; basal plate reduced; only a single
pair of proximal sclerites (PrxSc 1) associated with midsection; apical cone elon-
gate; posterior rami not distinct. Determined from Cook, op. cit.
Arrenurus lyriger
Fig. 11
Differs from A. crenellatus in being larger and more heavily sclerotized, as well as
proportionately more elongate. Anterior margin sclerite stronger; lateral wall of
proximal chamber supported by a pyriform sclerite; distal rod free from body of
EC in midsection; proximal arms short; basal plate small, triangular; proximal
sclerites (PrxSc 1-3) of midsection differ in number, size and shape; distal
arm sclerites heavily sclerotized; apical cone separated into two sections joined
only across anterior arch, more inflated and higher. Determined from Cook, op. cit.
Arrenurus magnicaudatus
Fig, 12
The EC of this species is larger, more elongate and more heavily sclerotized than
that of A. crenellatus. Anterior margin sclerite moderately sclerotized; proximal
margin of posterior keel strongly concave; distal rod free from body of EC in
midsection area; proximal arms longer; chamber ramus rudimentary; basal plate
small, crescentic, lying entirely distal to base of proximal arm; one elongate,
obliquely placed pair of proximal sclerites (PrxSc 1) in midsection; apical cone
narrower; distal arms and posterior rami distinct. Determined from Cook, op. cit.
Arrenurus major
Fig. 13
This species has the largest EC of any member of the genus examined. It is pro-
portionately more elongate and more heavily sclerotized than that of A. crenellatus.
Anterior surface of proximal chamber more strongly rotated counter-clockwise;
lateral walls strengthened by a small subtriangular sclerite; distal rod completely
free from posterior surface of EC; proximal arms heavier; basal plate lying entirely
distal to base of proximal arm; two pairs of spindle-shaped proximal sclerites
(PrxSc 1, 2) in midsection; distal arms well sclerotized, projecting farther laterally
so that base of apical cone flared broadly. Determined from Cook, op. cit.
Arrenurus planus
(not illus.)
The EC of this species is narrower than that of A. crenellatus and somewhat more
heavily sclerotized. Anterior margin sclerite more prominent; proximal arms
shorter and heavier; basal plate narrower and tongue-like; posterior keel reduced,
distal rod free from posterior surface of EC; two pairs of oblique sclerites (PrxSc
1, 2) present in midsection; anterior keel low, linear; apical cone small and propor-
tionately very short. Determined from Cook, op. cit.
af
PrxAm
Fig.
Fig.
Fig.
Fig.
28
BsPl
PrxSc 1
12
13
14
15
PrxSc 1
AntKl
DisAm
PosKl
DisAm
— PrxSc1
AntKl
DisAm
{ ———_ PrxAm
Arrenurus magnicaudatus: a, anterior view; b, lateral view.
Arrenurus major: a, anterior view; b, lateral view.
Arrenurus semicircularis: a, anterior view; b, lateral view.
Arrenurus trifoliatus: a, anterior view; b, lateral view.
Arrenurus semicircularis
Fig. 14
The EC of this species is about the same size as, but proportionately narrower
and shallower than that of A. crenellatus. Anterior surface of proximal chamber
less strongly rotated counter-clockwise; posterior keel much reduced; distal rod
completely free from posterior surface of EC, proximal arms stronger basally;
basal plate much reduced; only a single oblique proximal sclerite (PrxSc 1) in
midsection, anteroproximal tip expanded and subtriangular; apical cone narrow
and elongate. Determined from Cook, cp. cit.
Arrenurus trifoliatus
Fig. 15
This species has the EC less sclerotized, with most sclerites reduced in size and
complexity. Proximal chamber greatly expanded and produced proximally; anterior
margin sclerite reduced; lateral walls of chamber supported by a large subtriangular
sclerite; proximal arms short, heavy; distal rami prominent; basal plate absent;
posterior keel and distal rod absent; no sclerites in midsection: anterior keel low,
elongate; distal arm sclerites drastically reduced, represented only by two pairs of
sclerites lying distally in lateral walls of EC, homologies uncertain; no apical setae
observed. Determined from Wilson, 1961.
Arrenurus wardi
Fig. 16
The EC of this species is proportionately narrower and more elongate than that of
A. crenellatus and is also more heavily sclerotized. Proximal chamber smaller;
proximal arm heavier; basal plate reduced in size, extending proximally as a narrow,
curved strap; posterior keel truncate posteriorly; distal rod entirely free from
posterior surface of EC; a single pair of oblique proximal sclerites (PrxSc 1)
present in lateral walls of midsection, distoposterior tip expanded, club-shaped;
apical cone narrow and elongate. Determined from Cook, op. cit.
Atractides sp.
iis ly
The EC of this species is of the general Hydrodroma type but is more massively
built and more heavily sclerotized.
PROXIMAL CHAMBER square in anterior view, semicircular, with flat side facing
anteriorly in lateral view; anterior margin sclerite strongly chitinized, wide proxi-
mally in lateral view, interrupted midway by an ovoid excavation, tapering distally
to a blunt apex; no special strengthening sclerites in lateral walls; anteroproximal
margin of chamber drawn out medially to form a proximal ramus, expanded at
either end, wide in lateral view, narrow in anterior view; proximal horns absent.
POSTERIOR KEEL arises from convex posterior surface of chamber, proceeds
posteroproximally as a narrow bar, then expands into a large oval plate, sculptured
for muscle insertion; posterior keel gives rise to distal rod from posterodistal margin
of its narrow basal portion; rod curved, free from EC until level of anterior keel,
then closely applied to posterior surface, grading insensibly into distal membranes.
PROXIMAL ARMS massive, heavily sclerotized, strongly curved in anterior view,
projecting proximally to tip of proximal ramus, apices expanded, sculptured, with
margins finely divided for muscle attachment; distal rami strong; chamber ramus
29
PrxAm
PrxSc 1
Fig.
Fig.
Fig.
Fig.
30
AntKl
16
Ng
18
19
PrxHn
AntRm
AMScl
Cmb 2
Cmb 1
PrxSc 1
Cmb 4
Apcl
DisAm
Arrenurus wardi: a, anterior view; b, lateral view.
Atractides sp.: a, anterior view; b, lateral view.
Aturus (s. str.) sp. (nr. A. deceptor): a, anterior view; b, lateral view.
Axonopsis (Hexaxonopsis) sp.: a, anterior view; b, lateral view.
19a
18a
short, strong, grading into lateral chamber wall; a small, triangular basal plate
present in lateral chamber wall posterior to base of proximal arm.
MIDSECTION of EC largely membranous, supported primarily by a heavy, Y-
shaped proximal sclerite (PrxSc 1) on either side; this sclerite with base (long
arm) beginning posteriorly and running anteriorly, one short blunt inflated arm
projecting proximad as far as distal margin of proximal chamber, another longer,
thinner, apically expanded arm proceeding laterodistad to middle of anterior keel,
these sclerites especially prominent in anterior view; one pair of laterally-placed,
hook-shaped, distal sclerites (DisSc 1) aids in support of membranes of midsection
just proximal to distal arms, rod-like, distoproximally oriented, distal fifth tapering,
abruptly curved medially.
ANTERIOR KEEL Strongly sclerotized; arising from a long base and proceeding
anteriorly, first tapering, then expanding abruptly into a large, subtriangular plate
that is sculptured for muscle attachment; base supported by a thickened, sclero-
tized band travelling distally beneath anterior arch.
DISTAL ARMS massive, strong, heavily sclerotized, each projecting in a broad
arc laterally from body of EC, apices slightly expanded, sculptured, margins
divided for muscle attachment; anterior rami robust, apices apparently attached
but not fused medially; lateral shelf reduced to a small flange near base of distal
arm; posterior rami greatly expanded in lateral view, thickened basally in anterior
view, forming a partial support for lateral walls of distal portion of EC; no apical
development of distal arm sclerite; strong chitinous ligaments leading distad from
bases of distal arms appear to strengthen connections with distal membranes;
apical setae not noted.
Aturus (s. str.) sp.
(nr. A. deceptor) Fig. 18
The EC of this species is of the general Hydrodroma type.
PROXIMAL CHAMBER elongate in anterior view, widest midway, tapering distally
and proximally, greatly compressed anteroposteriorly, appearing narrow in lateral
view; anterior margin sclerite a thickened, sclerotized band, narrow proximally,
projecting beyond proximal wall, gradually broadening over strongly sinuate course
distad, grading gradually into lateral walls distally; no strengthening sclerites in
narrow, sclerotized, lateral walls; proximal horns absent.
POSTERIOR KEEL a Slight broadening of base of distal rod, attached to posterior
surface of proximal chamber proximal to base of proximal arms, rod tapered
gradually, curving distad beneath EC, apex joining posterior surface of EC again
at level of distal arm sclerites.
PROXIMAL ARMS broad basally, strongly curved, gradually tapering apically in
anterior view, Of subequal width and straight in lateral view; distal rami strong,
prominent in anterior and lateral views; chamber rami absent; basal plate absent.
MIDSECTION Of EC membranous; no proximal sclerites; a pair of small, sinuate,
spindle-shaped distal sclerites (DisSc 1) lie either side of base of anterior keel,
Sclerites narrow, angulate in anterior view; a single, median, lightly sclerotized,
semispherical chamber (Cmb 1) at base of anterior keel; three pairs of lateral,
membranous chambers (Cmb 2-4) visible in anterior view, largest, axillary pair
Cmb 4) semispherical, supported posteriorly by posterior rami of distal arm
sclerites.
ANTERIOR KEEL high, subtriangular in lateral view, much inflated, with a broad
base in anterior view, moderately sclerotized, continuous with membranous lateral
surfaces of EC.
at
DISTAL ARMS Slender, strong, well sclerotized, strongly curved, tapering apically;
anterior rami long, slender, pointed, strongly sclerotized, apices apposed medially;
posterior rami short, strong; each distal arm sclerite bears a flat, plate-like apical
development, subrectangular in lateral view, each bearing subapically a short simple
seta on lateral surface; lateral shelf forming part of posterior surface of distal-
most lateral outpocketing (Cmb 4).
Axonopsis (Hexaxonopsis ) sp.
Fig. 19
The EC of this species is of the general Hydrodroma type but is more compact
and heavily sclerotized.
PROXIMAL CHAMBER elongate in anterior view (1/2 length of EC), broadest at
bases of proximal arms, tapering rapidly distad, gradually proximad; chamber
strongly compressed anteroposteriorly, long and narrow in lateral view; lateral
walls narrow, heavily sclerotized; anterior margin sclerite a strong bar, V-shaped
in anterior view, bent at an angle of approximately 45° in lateral view, projecting
proximad beyond end of chamber, ending in a short, broad proximal ramus; proxi-
mal horns present, projecting laterally and posteriorly from lateral apices of
proximal ramus.
POSTERIOR KEEL attached to distal part of sclerotized posterior surface of
proximal chamber, elongate, anterior and posterior margins subparallel, tapering
distad to form a distal rod, produced posterad into a curved projection with
rounded apex; distal rod sinuate, attached to posterior surface of EC at level of
distal arm sclerites.
PROXIMAL ARMS short (projecting proximad only 2/3 length of proximal
chamber), heavily sclerotized, strongly curved in anterior view, with a wide, flange-
like lateral expansion from base, basal area broad in anterior view, tapering apically,
apex somewhat expanded, sculptured, margin divided for muscle attachment;
chamber ramus absent; distal ramus not prominent; basal plate large, pyriform,
rounded distally, grading insensibly into sclerotized lateral walls of midsection,
portion proximal to base of proximal arm tapering gradually, occupying most of
lateral surface of proximal chamber.
MIDSECTION of EC short, sclerotized laterally, membranous anteriorly and
anterolaterally; a lightly sclerotized, elongate, inflated sac (Cmb 1) arises on midline
anteriorly, just proximal to base of anterior keel; membranes of anterolateral area
doubly outpocketed (Cmb 2, 3) on either side; a compressed, sclerotized sac
(Cmb 4) subtends base of anterior keel on either side in axillary position, sub-
quacrate in anterior view.
ANTERIOR KEEL a right-angled triangle with hypotenuse facing anterodistally,
moderately sclerotized.
DISTAL ARMS strong, heavily sclerotized, crescent-shaped, tapering apically in
anterior view, almost straight in lateral view; anterior rami short with a thick
base, almost square in anterior view; posterior rami short, heavy; a small, trian-
gular lateral shelf joins base of distal arms to body of EC; apical setae absent.
Brachypoda (s. str.) sp.
(nr. B. cornipes) Fig. 20
The EC of Brachypoda is of the general Hydrodroma type but is more compact
and heavily sclerotized. Furthermore, the midsection displays a complex structure.
a2
PROXIMAL CHAMBER elongate, oval in anterior view, anteroposteriorly com-
pressed, narrow in lateral view; proximal and posterior walls heavily sclerotized,
lateral walls narrow, moderately sclerotized; anterior margin sclerite strong, heavily
sclerotized, U-shaped (in anterior view), curved (concave face anteriorly) in
lateral view, broadened and truncate proximally, ending in a small lobe on either
side distally, projecting proximad and anterad beyond proximal wall of chamber
as a quadrate proximal ramus; a proximal horn projects laterally on either side
from proximal ramus.
POSTERIOR KEEL attached to posterior side of proximal chamber, roughly
rhomboid, produced proximally into a short, triangular apex, tapering distally to
base of distal rod which travels straight, approximately parallel to longitudinal axis
of distal half of EC, tapering and grading imperceptibly into distal membranes.
PROXIMAL ARMS short, heavily sclerotized, curved, with laterodistal margins
expanded into a thin plate laterally, tapering apically in anterior view, tips slightly
expanded and sculptured; chamber ramus short and broad, articulating with distal
end of anterior margin sclerite; basal plate somewhat pyriform, broad distally,
grading insensibly into sclerotized lateral surfaces of EC, proximal part tapering,
acute, fused anteriorly with anterior margin sclerite.
MIDSECTION of EC with lateral walls lightly sclerotized, forming 4 main in-
flated chambers (Cmb 1-4) on either side; Cmb 3 more heavily sclerotized than
others, apparently incorporating lateral shelf into its structure; lateral walls
strengthened by a curved, pyriform, proximal sclerite (PrxSc 1) located distal to
distal tips of anterior margin sclerite on either side.
ANTERIOR KEEL Of extremely complex structure, composed of a distal and a proxi-
mal section; proximal section in form of an irregular cone lying on midline, tapered end
facing distally, broad end closed, facing proximally, composed of several overlapping,
inflated, sclerotized sacs with thickened, sinuate proximal surfaces in lateral view;
distal section composed of three structures arising from midline, distal-most laterally
compressed, high, T-shaped in anterior view, middle structure lower, somewhat
inflated, proximal structure still lower, inflated, wide in anterior view.
DISTAL ARMS long, strongly curved in anterior view, nearly straight in lateral
view, heavily sclerotized, apices expanded; anterior rami long, slender, heavily
sclerotized; lateral shelf forming part of Cmb 3; several ligaments arise from distal
edges of anterior rami and base of distal arms and appear to strengthen attach-
ment of distal membranes.
Eylais sp.
Fig. 21
The EC in Eylais is considerably different from the Hydrodroma type, although
most structures can be easily homologized. The body is largely membranous with
only isolated sclerotized structures.
PROXIMAL CHAMBER large (2/3 length of EC in anterior view, 1/2 of lateral
area), mostly membranous, somewhat variable in form; in anterior view main
(anterior) section of chamber oval (longitudinal axis laterally directed), with a
median proximal outpocketing; more posteriorly a pair of membranous out-
pocketings lie one on either side, each supported by a posterolateral extension of
anterior margin sclerite; in lateral view chamber high, posterior surfaces lightly
sclerotized; lateral walls largely membranous, supported by basal plate of proximal
arm sclerites and a semicircular sclerite articulated with, but posterior to, basal
plate; posterior margin of semicircular sclerite strengthened by a sclerotized rod
proceeding proximally to margin of chamber and terminating in a blunt apex; in
anterior view, anterior margin sclerite a long, curved (convex distally) rod with
i
Fig.
Fig.
Fig.
Fig.
34
20
2A
ja je
Me
Brachypoda (s. str.) sp. (nr. B. cornipes): a, anterior view; b, lateral view.
Eylais sp.: a, anterior view; 5, lateral view.
Forelia (Madawaska) borealis: a, anterior view; b, lateral view.
Frontipoda sp.: a, anterior view; b, lateral view.
expanded, subtriangular lateral apices (may correspond to proximal horns), lateral
apices then produced posterad and finally proximad, tips tapering, merging im-
perceptibly with membranous walls of chamber, sclerite thickened medially, giving
rise tO a proximally directed arm, straight, dilated apically; in lateral view, anterior
margin sclerite strongly S-shaped, median area high, arms curving posteriorly and
proximally.
POSTERIOR KEEL small, narrow, convex posteriorly; distal rod absent.
PROXIMAL ARMS long, slender, slightly curved in anterior view, sinuate in lateral
view, apices greatly expanded and sculptured for muscle attachment; medial rami
strong, straight, fused medially so that in anterior view proximal arm sclerites
appear as a single broadly curved bar (concave proximally); chamber ramus
directed distad, fused with a proximally directed ramus of distal arm sclerite;
basal plate large, subrectangular, strengthened by several sclerotized struts from
base of proximal arm, connected posteriorly by a strut to semicircular lateral wall
sclerite of proximal chamber.
MIDSECTION Of EC virtually eliminated by close juxtaposition of bases of proxi-
mal and distal arm sclerites; anterior side apparently open (opening of anterior
side of proximal chamber), membranes surrounding it joined distomedially to base
of anterior keel and laterally draped over bases of proximal arms to attach to
lateral walls of proximal chamber.
ANTERIOR KEEL large, subtriangular with apex truncate, broadly rounded, distal
margin supported by a thickened, broad, heavily sclerotized band that tapers distally
to support anterior wall of sperm passage, rest of structure less heavily sclerotized;
base of keel entirely fused with distal arm sclerites on either side.
DISTAL ARMS short, arising from base of anterior keel, proceeding laterad and
anterad on either side of keel, slender, heavily sclerotized, apices expanded and
sculptured; subtended by a complex basal sclerite that is attached posteriorly by a
strongly curved strut to basal plate of proximal arm sclerite; basal sclerite of distal
arms giving rise to struts that proceed distad strengthening lateral walls of sperm
passage, also posterad to semicircular sclerite. No other rami conspicuous; apical
setae absent. Area of sperm passage distal to distal arms roughly tubular with a
series Of pairs of weakly sclerotized strengthening rods in walls, most readily seen
in anterior view.
Feltria sp.
(not illus.)
This species possesses an EC too minute ( < 100 », ) for successful separation from
the large genital plate, and so detailed drawings could not be made. From limited
observations, the EC is clearly of the general Hydrodroma type. Proximal arms
well developed, proximal chamber heavily sclerotized only in proximal wall, distal
arms reduced in relative size.
Forelia (Madawaska ) borealis
Fig. 22
This EC has the typical Hydrodroma facies, differing primarily in the apical deve-
lopment of the distal arm sclerites. Determined from Cook, 1955b.
PROXIMAL CHAMBER elongate, subrectangular in anterior view, proximal margin
broadly rounded, high and curved in lateral view, posterior and proximal sides
elongate, anterior surface rotated counter-clockwise through approximately 30° with
respect to longitudinal axis of EC, facing anterodistally; proximal and posterior
a3
walls lightly sclerotized, semicircular in lateral view, no strengthening sclerites;
anterior margin sclerite a narrow, moderately sclerotized band, thickest and strong-
est along proximal margin; proximal horns project laterad from proximolateral
corners of anterior margin, each thin, strongly sclerotized, each a short, curved
(convex proximally) rod with a flange-like plate developed distolaterally.
POSTERIOR KEEL small, linear, attached basally to posterior surface of chamber
midway along its length, projecting proximad a short way parallel to longitudinal
axis of EC; no distal rod; membranes along posterior surface of EC proximal to
bases of distal arms containing an elongate, sclerotized rod that may correspond
to distal section of distal rod.
PROXIMAL ARMS shorter than proximal chamber, strong basally, well sclerotized;
chamber ramus short and indistinct; distal ramus well developed; no basal plate.
MIDSECTION Of EC bearing proximally a pair of sclerotized plates (PrxSc 1)
forming in anterior view, a U-shaped structure (convex distally) delimiting distal
boundary of membranes of anterior surface of proximal chamber; lateral surfaces
of midsection lightly sclerotized, inflated to form two chambers on either side;
proximal-most chamber (Cmb 1) of small diameter, incorporating no other sclerites;
more distal chamber (Cmb 2) large, supported mainly by posterior ramus and
lateral shelf of distal arm sclerite; in lateral view, just above Cmb 2 is a narrow,
spindle-shaped sclerite (DisSc 1) in lateral wall.
ANTERIOR KEEL not higher than anterior arch, anterior margin dissected, ir-
regular, roughly rectangular, tapering distally, passing beneath anterior arch,
merging with anterior wall of sperm passage.
DISTAL ARMS short, strong, heavily sclerotized, straight, projecting at an angle
of 40° to longitudinal axis of EC in anterior view, strongiy curved (convex poste-
riorly) in lateral view; continuous with high, triangular anterior ramus; area
distal to these arms expanded (apical development), entire basal area of distal
arm sclerite subtriangular in lateral view; posterior ramus strong, proximal portion
strongly curved (convex laterally and posteriorly), supporting distal-most lateral
chamber (Cmb 2); lateral shelf well developed.
Frontipoda sp.
Fig. 23
Only one species of Frontipoda (F. americana) has been described from North
America. However, genitalic dissections during the course of this study have
revealed the presence of two different forms, so that a specific name will not be
applied to the population described here.
The EC is more compact than that of Hydrodroma and most structures are
reduced in relative size and degree of sclerotization.
PROXIMAL CHAMBER elongate in anterior view, subrectangular, narrower distally,
wider and rounded proximally; in lateral view chamber high, subrectangular, a
distinct angle between posterior and proximal surfaces; in lateral view, proximal
and posterior walls only moderately sclerotized as are lateral walls; anterior margin
sclerite a narrow sclerotized band, U-shaped in anterior view; distal ends of margin
sclerite produced posteriorly to form well-defined, sclerotized, distolateral borders
of chamber, these sclerites then curving distally to merge with Jateral walls of
midsection of EC; proximal horns absent.
POSTERIOR KEEL inflated, clearly an extension of cavity of proximal chamber,
subtriangular, attached broadly to posterior side of chamber, curved and tapered
distally to give rise to distal rod travelling straight distally to level of apex of EC
where it grades gradually into distal membranes.
36
PROXIMAL ARMS short, stubby, wide in anterior view, expanded at apex, pro-
jecting at approximately 55° to longitudinal axis of EC; chamber ramus short,
articulating with sclerotized distolateral border of chamber; an angular basal plate
lies at base of proximal arms in lateral wall of EC, primarily distal to base of
proximal arm, strengthened by two sclerotized struts from base of this arm.
MIDSECTION Of EC lightly sclerotized, inflated to form a pair of large lateral
chambers (Cmb 1); a series of parallel, distoproximally oriented, sclerotic ridges
subtend anterior keel on either side; no other conspicuous sclerites.
ANTERIOR KEEL subtriangular, Occupying approximately distal half of EC,
supported and strengthened by a sclerotized anterodistal edge, proximal margin
rounded, broad in anterior view.
DISTAL ARM sclerites much reduced, apparently represented by two small,
spindle-shaped sclerites situated laterally on either side of distal end of EC, visible
in anterior view.
Geayia sp.
Fig. 24
The EC of this species is easily referable to the Hydrodroma type, but the pro-
portions of various areas are altered, and there is considerable apical development
of the distal arm sclerites.
PROXIMAL CHAMBER Oval in anterior view, widest at ends, narrower at mid-
length, rounded distally and proximally; in lateral view subrectangular, rotated
counter-clockwise through approximately 30°, anterior surface faces anterodistally;
anterior margin sclerite a thickened, sclerotized band, oval in anterior view, in
lateral view projecting proximad beyond end of proximal chamber, joined to chamber
by an anteroproximal extension of proximal wall; lateral chamber walls supported and
strengthened by a heavy, well-sclerotized, oblique, lateral wall sclerite, fused proxi-
moanteriorly with anterior margin sclerite, articulated posterodistally with base of
proximal arm; proximal horns present, arising on either side from proximolateral
corners of anterior margin sclerite, short, slender, straight in lateral view, curved
in anterior view, slightly expanded at tips.
POSTERIOR KEEL attached broadly to posterior surface of proximal chamber
midway along its length, expanding greatly to form a large, reniform plate, rounded
proximally, tapering distally to give rise to a strongly curved, sclerotized, distal rod;
distal rod sinuate, separate from body of EC through most of its length, proceeding
anterad to lie immediately below EC at level of anterior keel.
PROXIMAL ARMS Of medium length, broad, massive in anterior view, not pro-
ceeding proximad beyond proximal horns, strongly curved (convex posteriorly) in
lateral view, apices little expanded, lateral margin expanded to form a thin,
sculptured plate for muscle attachment; chamber ramus short, curved, closely asso-
ciated with distal tip of lateral wall sclerite; distal ramus strong, proceeding distad
to level of anterior keel.
MIDSECTION Of EC with lateral walls lightly sclerotized, supported by heavily
sclerotized rods and plates (PrxSc 1-3), anterior surface in this area membranous;
structure of supporting sclerites most clearly seen in anterior view; most anteriorly
lie a submedial pair of Y-shaped sclerites (PrxSc 1); lying below Y-shaped sclerite,
a Sinuate sclerite (PrxSc 2) proceeding distad irregularly from laterodistal corner
of margin sclerite, ending in an enlarged, irregular, blunt apex; a pair of small
submedian sclerites (PrxSc 3) lie slightly proximal to proximal margin of anterior
keel; lateral walls of midsection inflated to form a median, elongate, rounded tube
(CMb 1) subtending anterior keel.
a0
a
w“
[-*]
ae!
nN
N
me}
= nN
a) Uo = £ - AN
a “w 2 = N
a RE r Boexgne &
a VU a BE Rok Ein
Vaava e
Fig. 24 Geayia sp.: a, anterior view; b, lateral view.
Fig. 25 Hydrachna (Rhabdohydrachna) sp.: a, anterior view; b, lateral view.
Fig. 26 Hydrovolzia sp.: a, anterior (?) view, distal end at top; b, lateral view,
proximal end at top.
Fig. 27 Hydryphantes sp. (nr. H. ruber): a, anterior view; b, lateral view.
38
ANTERIOR KEEL large, well-sclerotized, subrectangular in lateral view, anterior
surface rounded, irregular, strengthened by lightly sclerotized anterior and distal
margins, part of proximal and posterior margins strengthened and supported by a
strongly sclerotized, curved band that continues distad, tapering beneath anterior
arch.
DISTAL ARMS short, strongly curved in anterior view, wide at base; in lateral
view, almost straight; anterior ramus long, strong, heavily sclerotized, tips of two
anterior rami not apposed medially but joined by a strong chitinous band or liga-
ment; posterior rami strong, heavily sclerotized, projecting proximally to level of
proximal margin of anterior keel; lateral shelf broad, produced proximally to
form a quadrate, proximally truncate plate joining distal arm to posterior ramus,
margins strengthened by sclerotized thickenings; base of distal arm sclerite gives
rise to an apical development, moderately sclerotized, apparently lying along lateral
wall of sperm passage, approximately tubular, provided with a subdistal, simple
apical seta.
Hydrachna (Rhabdohydrachna) sp.
Fig. 25
The EC of this species is of the general Hydrodroma type modified by heavier
sclerotization of the proximal chamber and midsection, and reduction in size and
complexity of the distal arm sclerites.
PROXIMAL CHAMBER elongate, rectangular in anterior view, subquadrate in lateral
view, walls heavily sclerotized, membranes of anterior surface thick and leathery;
anterior margin sclerite not prominent, anterior section of distolateral border of
chamber strongly sclerotized, continuous with proximal sclerite (PrxSc 1) of mid-
section; proximal horns absent.
POSTERIOR KEEL a broad curved plate attached at one end to posterior surface
of proximal chamber, projecting posteriorly and distally; no distal rod present.
PROXIMAL ARMS massive, heavily sclerotized, strongly curved; chamber ramus
short, grading into sclerotized lateral wall of proximal chamber, distal ramus
strong, fused with sclerotized lateral and posterior walls of midsection; basal plate
well developed, forming part of sclerotized lateral surface of EC.
MIDSECTION of EC sclerotized on all surfaces; strengthened by pair of proxi-
mal sclerites (PrxSc 1) that are narrow, sinuate anteriorly, broad, well sclerotized
and V-shaped laterally, continuous proximally with distolateral border of proximal
chamber; these sclerites support a pair of conical lateral chambers (Cmb 1).
ANTERIOR KEEL with a narrow, elongate, anterior projection and inflated basal
section passing along anterior surface of EC.
DISTAL ARMS reduced, short, straight; anterior rami rudimentary, only lightly
sclerotized, anterior arch low; other rami much reduced; no apical setae.
Hydrovolzia sp.
Fig. 26
Only a few alcohol-preserved specimens of this species were available for study,
and no completely satisfactory skeletal preparations could be made. The EC is
small and difficult to manipulate, and the alcohol preservation rendered the muscle
tissue refractory to ordinary clearing agents. The sclerotized structures were not
examined in detail, but Fig. 26 gives a general impression of the configuration.
Except for an elongate pair of proximolateral sclerites, perhaps analogous to the
39
proximal arms, there appears to be no structural similarity to the Hydrodroma EC.
This genus may be more easily homologized with the Trombidioidea than
with the water mites, Once its structure is better understood.
Hydryphantes sp.
(nr Hs yuber)) Figs 27
The EC of Hydryphantes resembles, in general, that of Hydrodroma, although the
distal arm sclerites are reduced.
PROXIMAL CHAMBER Subrectangular in anterior and lateral views, anterior sur-
face wider than posterior section which tapers distally, posterior and proximal
walls smoothly rounded, moderately sclerotized, as are lateral walls; no strengthen-
ing sclerite in lateral walls; anterior margin sclerite a thickened, sclerotized band,
smoothly rounded proximally in anterior view, in lateral view proceeding distally
parallel to longitudinal axis of EC, curving abruptly posterad at approximately 90°,
forming strong, anterodistal shoulder of proximal chamber; distal tips of anterior
margin sclerite project posterad and distolaterad forming strong distolateral borders
of proximal chamber, greatly expanded apically; proximal horns absent, anterior
margin sclerite of anterior surface produced proximally on midline into a small
proximal ramus projecting anterodistad, narrow in lateral view, wider in anterior
view, expvanded proximally.
POSTERIOR KEEL a slight broadening of base of sinuate distal rod, attached to
posterior surface of proximal chamber near its distal end.
PROXIMAL ARMS broad, strong, heavily sclerotized, strongly curved in anterior
view, projecting proximad beyond tip of proximal ramus, slightly sinuate in lateral
view; chamber ramus absent; distal ramus strong, curved, proceeding distally to
midway along anterior keel; a subrectangular basal plate present, lying in lateral
wall of proximal chamber, produced proximally to an acute, anteroproximal apex.
MIDSECTION of EC largely membranous proximally with two main pairs of
sclerites (PrxSc 1, 2); anterior-most (PrxSc 1) L-shaped, one arm from each side
joined anteriorly to form a raised, irregular, median projection; posterior-most
sclerite (PrxSc 2) also roughly L-shaped, an inflated, sclerotized fold of lateral
wall, anteriorly directed arm also fused with median projection, lateral surfaces
sculptured for muscle attachment; a pair of lateral chambers (Cmb 1) supported
by distolateral border sclerite of proximal chamber, another by proximal sclerites
of midsection (Cmb 2); distal area of midsection a lightly sclerotized tube.
ANTERIOR KEEL elongate, roughly oval, anterior margin irregular, divided, proxi-
mal section of anterior margin elevated into a rounded projection strengthened by an
anterior sclerotized thickening base of keel supported by a thickened, sclerotized
band.
DISTAL ARMS short, spindle-shaped, almost straight in anterior view; anterior
rami short, slender, strongly sclerotized, apices apposed on midline; posterior
ramus strong, sinuate, spindle-shaped, proximal apices curving laterad to aid in
support of Cmb 2; lateral shelf absent.
Hygrobates sp.
Fig. 28
This species has an elaborate EC of the general Hydrodroma type.
PROXIMAL CHAMBER Subrectangular in anterior view, anteroposteriorly com-
pressed, narrow in lateral view, posterior side strongly sclerotized, proximal side
40
less so, lateral walls lightly sclerotized, anterior surface largely membranous;
margins of anterior surface supported and strengthened by a narrow, thin, strongly
sclerotized margin sclerite, broadly U-shaped in anterior view, produced proximally
on median line to form a median proximal ramus which is straight, anteroproxi-
mally directed, expanded, bearing a pair of rudimentary proximal horns apically;
margin sclerite of anterior surface dips posterad on either side into a broadly U-
shaped excavation of lateral wall, membrane bridges this gap.
POSTERIOR KEEL elongate, bilobed; smaller proximal lobe rounded proximally,
proximal margin lightly sculptured, keel attached to distal part of posterior surface
of proximal chamber by a broad stalk; distal lobe large, tapering distally to a
curved distal rod; distal rod free from posterior surface of EC, grading distally into
distal membranes.
PROXIMAL ARMS project at almost 90° to body of EC basally, then bent proxi-
mad at almost 90°, straight, strong, wide, heavily sclerotized, expanded greatly at
apices to form a thin, sculptured apical plate for muscle attachment; chamber
ramus absent; distal ramus well developed; no basal plate.
MIDSECTION of EC moderately sclerotized laterally and posteriorly, primarily
membranous anteriorly, strengthened and supported by two pairs of large, heavy
sclerites; proximally, an anteroposteriorly directed rod (PrxSc 1) with a twisted,
sculptured anterior arm on either side; distally, expanded anterior tips of paired
L-shaped sclerites (DisSc 1) also project above anterior surface; both pairs of
sclerites support folds of membranous anterior surface; a pair of posterolateral
chambers (Cmb 1) formed by inflation of sclerotized lateral walls, an axillary pair
of chambers (Cmb 2) strengthened by L-shaped sclerites (DisSc 1) and posterior
rami Of distal arm sclerites.
ANTERIOR KEEL narrow laterally and distoproximally, high, rounded apically,
proximal margin angulate, distal margin sinuate, base subtended by a pair of sinuate,
strongly sclerotized bars with proximal tips produced anteriorly and_ strongly
hooked.
DISTAL ARMS long, strong, heavily sclerotized, almost straight in lateral view,
in anterior view strongly curved, tapering regularly to apices, apices little expanded;
anterior rami broad in anterior view; posterior ramus moderately strong, produced
proximad to level of proximal margin of anterior keel; no apical development or
apical setae.
Koenikea sp.
ie 29
The EC skeleton is of the general Hydrodroma type and is relatively simple in
structure.
PROXIMAL CHAMBER circular in anterior view, subquadrate in lateral view;
posterior and proximal walls moderately well sclerotized as are lateral walls; lateral
and proximal margins of anterior surface supported and strengthened by a strong,
heavily sclerotized, semicircular margin sclerite, thick and broad proximally, distal
apices tapering, attenuate; proximally on midline, margin sclerite drawn out into
a short, broad, almost square proximal ramus, directed anteroproximad in lateral
view; an elongate, curved (convex proximally) proximal horn arises from each
proximolateral corner of proximal ramus.
POSTERIOR KEEL narrow, elongate posteriorly, basal section narrower, stalk-like,
expanding apically into a broader plate that is irregular proximally and tapers
distally to form a narrow, strongly sclerotized, smoothly curved (convex posteriorly )
distal rod; rod free from body of EC, merging abruptly with distal membranes
below EC at level of distal arm sclerites.
4]
Hygrobates sp.: a, anterior view; 5, lateral view.
Koenikea sp.: a, anterior view; b, lateral view.
Kongsbergia sp.: a, anterior view; b, lateral view.
Lebertia sp.: a, anterior view; 5, lateral view.
PROXIMAL ARMS strong, curved, heavily sclerotized, broad in anterior view;
tips expanded, little sculptured; chamber ramus short, broad, heavy; distal ramus
strong, well-developed, projecting distad to level of distal-most section of anterior
keel; basal plate small.
MIDSECTION of EC with anterior and lateral surfaces moderately sclerotized,
more membranous anteriorly; three pairs of lateral chambers form most prominent
feature of area; proximal-most two chambers (Cmb 1, 2) merely semisclerotized
outpocketings of wall; distal-most chamber (Cmb 3) with a moderately well-
sclerotized, strongly curved (convex proximally) proximal wall, anterior and dis-
tolateral walls largely membranous.
ANTERIOR KEEL divided into two sections; proximal-most lying approximately
midway along length of EC, short and narrow, basal stalk projecting anteroproxi-
mally, then expanding into a subcircular sculptured plate; distal-most section of
keel wider, subrectangular, anterior margin convex but irregular, anterior area
sculptured for muscle insertion; no prominent sclerotized supports for either section
of anterior keel.
DISTAL ARMS strong, well-sclerotized, sinuate, tapering only gradually to curved,
acute apices; anterior rami long, sinuate, in lateral view broad basally, rapidly
tapering apically, apices apposed anteriorly on median line; posterior ramus short,
broad, subtriangular in lateral view; lateral shelf absent; no apical setae present.
Kongsbergia sp.
Fig. 30
The EC of this species is similar to the basic Hydrodroma type.
PROXIMAL CHAMBER Oval in anterior view, in lateral view anteroposteriorly
flattened, narrow, subrectangular, anterior surface entirely membranous, posterior
and proximal walls heavily sclerotized, lateral walls only moderately sclerotized;
lateral and proximal margins strengthened and supported by a. narrow, heavily
sclerotized anterior margin sclerite, thicker proximally, tapering distally, projecting
proximad as an over-hanging lip (rudimentary proximal ramus) beyond proximal
end of chamber; no strengthening sclerites in lateral walls of chamber; proximal
horns lacking.
POSTERIOR KEEL elongate, narrow, broadly attached to posterior surface of
chamber, posterior and proximal margins irregular, tapering distally to form a
strong, weakly curved (convex posteriorly), well-sclerotized distal rod; distal
rod free from EC through most of its length, becoming closely associated with
posterior surface distal to distal arm sclerites.
PROXIMAL ARMS massive, strongly curved, heavily sclerotized, projecting proxi-
mad to apex of proximal chamber, basal areas broad, tapering rapidly to slightly
expanded apices, sculptured for muscle insertion; chamber ramus absent; distal
ramus strong, well developed.
MIDSECTION Of EC elaborate in structure; primarily membranous anterior sur-
face supported by three main sclerites; centre sclerite (PrxSc 1) distoproximally
Oriented, shaped as a tall letter “V” with truncate apex, arms of “V” concave
laterally, forming anterolateral margins of anterior surface of proximal chamber;
surrounded by this sclerite and more proximally placed, a tall, omega-shaped
sclerite (PrxSc 2); distal-most of anterior sclerites (DisSc 1) forms a structure
roughly reniform in anterior view, convex margin facing distally, two short,
curved rami on either side; in lateral view anterior sclerites narrow, elevated, plate-
like in form, anterior margins strengthened by sclerotized thickening; omega
sclerite (PrxSc 2) elevated distally to a level equal to that of apices of anterior
43
arch; V-shaped sclerite (PrxSc 1) elevated proximally: reniform sclerite (DisSc 1)
not distinctly visible in lateral view; in anterior view lateral surfaces of midsection
of EC inflated into a pair of lateral chambers (Cmb 1) on either side, form
irregular, walls lightly sclerotized.
ANTERIOR KEEL absent, its morphological position and function apparently
assumed by anterior projections of proximal-most two anterior surface sclerites
(PrexSey 2
DISTAL ARMS strong, heavily sclerotized, strongly curved in anterior view,
broad basally, tapering gradually to lightly sculptured apices, margins divided for
muscle insertion, almost straight in lateral view, expanded slightly; anterior ramus
slender, especially in anterior view, tapering to an acute apex, curved proximally in
lateral view; posterior rami situated in lateral wall apparently as a strengthening
structure, elongate, inflated basally, narrower towards expanded, blunt apex; a broad
subtriangular section of posterior ramus present in lateral wall; lateral shelf absent;
apical setae lacking.
Lebertia sp.
Fig. 31
The EC of this species shows a typical Hydrodroma structure but is more compact,
heavily sclerotized, and complex.
PROXIMAL CHAMBER Oval in anterior view; in lateral view high, short disto-
proximally, posterior and proximal walls moderately sclerotized, lateral walls lightly
sclerotized; lateral walls strengthened by an oblique sclerite that articulates disto-
posteriorly with base of proximal arm sclerite and is free anteroproximally; anterior
surface largely membranous, lateral and proximal margins supported and strength-
ened by a thickened, broadly U-shaped margin sclerite, in anterior view of sub-
equal width all way around, distal tips indistinct; in lateral view, distal arms of
margin sclerite narrower proximally, broader distally, forming a distal shoulder,
then directed posterad to form a broad, sclerotized distolateral border of proximal
chamber, border sclerite fused with base of proximal arm, then sweeping distally
along lateral wall of midsection of EC; proximal horns arise from proximal margin
of anterior margin sclerite, bases fused, each large, broad, tapering to a blunt
apex, curved (convex proximally), produced laterally so that apex almost apposed
with proximal apex of proximal arm.
POSTERIOR KEEL elongate, narrow, roughly a curved oval, posterior and proximal
margins sinuate, irregular, abruptly tapering distally to form a sinuate, strongly
sclerotized distal rod that curves first posterad then abruptly anterad to follow
general contour of posterior surface of EC, distal tip of rod closely associated
with posterior surface of EC just distal to level of distal arm sclerite.
PROXIMAL ARMS short, weakly curved in anterior view, heavily sclerotized,
widest basally, tapering to a blunt, rounded apex, sinuate, tapering in lateral view;
chamber ramus indistinct; distal ramus strong, well developed, especially in lateral
view; a subtriangular basal plate present, lying primarily distal to base of proximal
arm.
MIDSECTION of EC lightly sclerotized, some small membranous areas anteriorly;
main feature of this region in lateral view an oblique, lateral sclerite (DisSc 1)
oriented from anteroproximal to posterodistal in lateral wall, a wide, heavily scle-
rotized band, sides subparallel, posterior side merging with lateral wall of EC,
anterior side raised to form an elongate ridge, anteroproximally giving rise to a
short, broad rod articulating with distal shoulder of anterior margin sclerite,
posterodistally giving rise to a strong, laterally directed axillary arm that is
expanded apically, sculptured for muscle attachment, and articulated with apex of
44
distal arm; anterolateral area of this section of EC greatly elevated, inflated, in
anterior view an elongate pyriform anterior chamber (Cmb 1), rounded distally.
tapering to an acute apex proximally.
ANTERIOR KEEL low, elongate, curved (convex anteriorly), truncate posteriorly,
lying along median line of proximal half of anterior pyriform chamber (Cmb 1).
DISTAL ARMS strong, broad basally, heavily sclerotized, slightly curved (concave
laterally) in anterior view, apices expanded, especially laterally, sculptured for
muscle attachment; anterior ramus short, subtriangular, with rounded apex, apices
of two sides apposed on midline; posterior ramus large, strongly curved (concave
posteriorly), tapering proximally, apparently partially fused with distal ramus of
proximal arm sclerite, proximal half free from body of EC; small, subtriangular
lateral shelf joins distal arms to proximomedial rami and body of EC; apical setae
not observed.
Limnesia (s. str.) sp.
Fig. 32
The EC of this species represents one of the most extensive elaborations of the
basic Hydrodroma type observed in the present study.
PROXIMAL CHAMBER large, subrectangular in anterior view; posterior wall weakly
curved; proximal wall high, so that anterior surface rotated counter-clockwise
through approximately 50° with respect to longitudinal axis of EC; lateral wall
strengthened by a narrow, curved sclerite, obliquely placed, anteroproximal end
fused with anterior margin sclerite, posterodistal end articulating with chamber
ramus of proximal arm sclerite; lateral and proximal margins of anterior surface
supported and strengthened by a narrow, broadly rounded, anterior margin sclerite,
tapering to apices distally, somewhat thickened proximally, giving rise to a short,
blunt proximal horn at each proximolateral corner.
POSTERIOR KEEL large, elongate, broadly attached to posterior side of proximal
chamber, produced proximally into an irregular subtriangular plate, tapering distally
to form a narrow, strongly sclerotized, curved (convex posteriorly) distal rod;
distal rod free from EC throughout most of its length, closely associated with
posterior surface distally at level of distal arm sclerites.
PROXIMAL ARM broad basally, almost straight in anterior view, tapering apically,
apex expanded, blunt, sculptured for muscle insertion; chamber ramus prominent,
sinuate, directed anterodistally; distal ramus strong, heavily sclerotized, broad
basally in anterior view.
MIDSECTION of EC; sclerites of anterior surface include a laterally-convex, nar-
row band (PrxSc 1) forming distal and distolateral margins of anterior surface of
proximal chamber; distal to this sclerite lies a pair of submedian, bipartite sclerites
(DisSc 1), in lateral view proximal portions of bipartite sclerites form an anterior
subrectangular projection with truncate apex, arising proximal to base of anterior
keel; final major sclerite an oblique strap in lateral wall (DisSc 2), giving rise dis-
tally to a strong, laterally directed axillary arm, evident in anterior view; lateral
arm Of DisSc 2 supports membranes forming an irregular axillary chamber (Cmb 1).
ANTERIOR KEEL Ssubtriangular, high, margins irregular, apex rounded, curved
proximally, proximal margin concave, surface sculptured for muscle attachment.
DISTAL ARMS broad, strong, heavily sclerotized, margins subparallel, tapering
acutely only in apical section to a blunt apex; anterior ramus short. subtriangular,
broad basally, rounded apically, almost square in anterior view, apices apposed
but not connected on median line; lateral shelf replaced by an expanded axillary
knob; each distal arm sclerite gives rise to a short, conical, lightly sclerotized
apical development, bearing a short, strong apical seta.
45
L2S*4d
wy Xd
Zw 2S5!0
L>ss!d
L2SX4d
puuy
quia xd
INSOd
b, lateral view.
a, anterior view; b, lateral view.
Fig. 33. Limnochares sp. (nr. L. americana): a, anterior view;
a, anterior view; b, lateral view.
a, anterior view; b, lateral view.
Fig. 32 Limnesia (Ss: str:) sp::
Fig. 34 Midea sp.:
Fig. 35 Mideopsis sp.:
46
Limnochares sp.
(nr. L. americana) Fig. 33
The EC skeleton of Limnochares is little modified from a sclerotized tube and
possesses fewer well-defined sclerites than that of Hydrodroma. In anterior view,
two main sections are distinguished: a wide, subrectangular proximal section com-
posed primarily of proximal chamber and proximal arm sclerites, and distally, a
narrower tube, corresponding to distal portion of sperm passage, walls lightly
sclerotized, some distal thickenings representing rudiments of distal arm sclerites
but otherwise featureless.
PROXIMAL CHAMBER Subrectangular in anterior and lateral views, chamber walls
lightly sclerotized, anterior surface membranous, no prominent margin sclerite;
lateral wall of proximal chamber strengthened by an array of sclerotized bands and
narrow, sclerotic, surface ridges; in lateral view margins of proximal chamber
constricted at various points suggesting division of chamber into cavities, some
of which may function in semen retention or spermatophore formation; proximal
horns absent.
POSTERIOR KEEL joined to body of EC in an unusual way; supported by a
subtriangular sclerite in lateral wall of EC distal to proximal chamber, attached to
these sclerites by a long, curved stalk, projecting as a subtriangular plate below
posterior surface of chamber, margins irregular; no distal rod.
PROXIMAL ARMS short and curved in anterior view, not projecting proximad
beyond apex of proximal chamber, basal area broad and fused with sclerotized
lateral walls of chamber; a distinct basal plate not discernable; chamber ramus
projects distally and anteriorly, joins with a rudiment of anterior arch of distal arm
sclerites; medial rami present as short, thick, blunt, medial projections apposed
on median line.
MIDSECTION Of EC much reduced as anterior keel positioned immediately distal
to proximal chamber; lateral surfaces without distinct sclerotized areas, strengthened
by several sclerotic surface ridges.
ANTERIOR KEEL subtriangular, proximal margin sinuate, step-like, thickened by a
sclerotized band, distal margin slopes concavely, proceeds distad to participate in
formation of anterior wall of distal tube, apex blunt.
DISTAL ARM sclerites represented by sclerotizations situated on anterior surface
of EC distal to anterior keel, (cf. basal sclerite of distal arms in Eylais), in lateral
view appearing as a strongly arched sclerite, anterior margin supported by a
thickened sclerotized band, continuous with chamber ramus of proximal arm
sclerite, lateral surface strengthened by a sclerotic ridge curving posteriorly and
proximally to fuse eventually with base of proximal arm sclerite; a more distal
series Of sclerotized folds partially surrounding distal tube not easily homologized
with any structure in Hydrodroma EC.
From base of anterior keel and from base of proximal arm, run curved,
strongly sclerotized rods that fuse distally and proceed forward as an anterior,
internal rod, along length of sperm passage; on posterior side lie a pair of curved,
spindle-shaped, rods, attenuate distally, broadened and truncate proximally, may be
homologous with distal-most of distal sclerites of Hydrodroma.
Midea sp.
Fig. 34
The EC of Midea is greatly modified but is basically similar to that of Hydrodroma.
PROXIMAL CHAMBER in anterior view oval, slightly compressed, narrowed in
47
midlength, rounded anteriorly and posteriorly; in lateral view subrectangular, margins
and corners smoothly rounded; lateral, proximal, and posterior walls of chamber
lightly sclerotized; anterior surface primarily membranous; anterior margin sclerite
strongly rounded, U-shaped, thicker along proximal margin, tapering distally on
either side; on midline proximally a strong, proximal ramus produced, bifurcate at
apex, each part of bifurcation short, subtriangular, blunt at apex, representing a
rudimentary proximal horn.
POSTERIOR KEEL rudimentary, partially membranous, incorporating a small,
irregular sclerite centrally; distal rod absent.
PROXIMAL ARM Sclerites set more distally on EC than in Hydrodroma, base lying
distal to distal side of proximal chamber; proximal arms strong, heavily sclerotized,
strongly curved in anterior view, not reaching proximally to apex of proximal
chamber; chamber ramus produced anteriorly and proximally, greatly expanded into
a subtriangular sclerite strengthening lateral part of proximal and posterior walls
of proximal chamber; distal rami strong, well sclerotized, proceeding forward
slightly distal to distal arm sclerites; basal plate lying distal to base of proximal
arm.
MIDSECTION of EC distal to proximal chamber primarily membranous; in
lateral view, three small sclerites (PrxSc 1-3) support this area; PrxSc 1 irregular,
forming a distal margin to anterior surface of proximal chamber; in anterior view
membrane outpocketed into two median chambers (Cmb 1, 2); most proximal
(Cmb 1) lying immediately distal to proximal chamber and supported in part by
PrxSc 1 sclerites; distal-most chamber (Cmb 2) subtends base of anterior keel;
two indistinct lateral chambers also evident in anterior view.
ANTERIOR KEEL rudimentary, partially membranous, in lateral view appearing
as two distinct structures, each one a short, narrow plate projecting anteriorly from
anterior surface of EC.
DISTAL ARM sclerites much modified; anterior ramus and base of sclerite appear
fused and expanded to form a small, cone-shaped apical development, apices of cones
sculptured and excavated for muscle insertion; distal arm projects laterad and
proximad as a small, curved, smoothly tapering, rod-like sclerite; no trace of
posterior rami; a small lateral shelf joins base of distal arm to cone section of
sclerite; apical setae not present on this sclerite.
Mideopsis sp.
Fig. 35
The EC of this species is clearly of the Hydrodroma type, although the distal
section is greatly modified.
PROXIMAL CHAMBER narrow, suboval in anterior view, long, narrow, antero-
posteriorly compressed in lateral view; anterior surface primarily membranous,
supported and strengthened by a strong, U-shaped margin sclerite, broad and
heavy proximally, tapering distally, in lateral view margin sclerite strong, well
sclerotized; in addition to following margin of anterior surface, margin sclerite has
a posterior projection in lateral wall of proximal chamber almost to base of
proximal! arm sclerite, apex of this projection produced laterad, visible in anterior
view; lateral, proximal, and posterior walls well sclerotized; anteroproximally a
club-shaped lateral wall sclerite visible in lateral view, broad thickened end articu-
lating with proximal end of anterior margin sclerite, more attenuate and paralleling
posterior projection from margin sclerite, passing under it in wall of chamber and
ending slightly distal to its apex; a proximal horn projects anterad from either
proximolateral corner of anterior margin sclerite, each a short, stout, heavily
sclerotized rod, apex expanded, sculptured for muscle insertion.
48
POSTERIOR KEEL attached to rounded, inflated apex of proximal chamber which
is produced proximally, keel produced posteriorly from chamber as a narrow plate,
tapering gradually distally, giving rise to a sinuate distal rod; distal rod free
from body of EC throughout most of its length, closely associated with posterior
surface only in area of distal arm sclerites.
PROXIMAL ARMS massive, strong, heavily sclerotized, short, straight in anterior
view, projecting at an angle of approximately 35° to longitudinal axis of EC,
apices greatly expanded, subtriangular, curved medially, not extending proximally
beyond apex of proximal chamber; chamber ramus absent; distal ramus strong,
well sclerotized; basal plate greatly developed, elongate in distoproximal direction,
occupying posterior half of lateral wall of proximal chamber and part of proximal
and posterior walls.
MIDSECTION of EC lightly sclerotized and elaborate, no well-defined sclerites
strengthening walls, a number of sclerotized outpocketings and a number of surface
sclerotic ridges serve to make area rigid and give it form.
ANTERIOR KEEL low, anterior margin sinuate, lateral surface heavily sculptured,
supported basally by several surface sclerotic ridges, bifurcate proximally in
anterior view.
DISTAL ARMS short, massive basally, tapering rapidly to an expanded apex,
strongly curved, apices sculptured with divided margins for muscle attachment;
anterior rami slender, tapering gradually to apex, rami of either side completely
fused on midline so that anterior arch continuous; region distal to anterior arch
and distal arm greatly expanded, in lateral view a high, broad, anterior section
supported by a narrow, oval margin sclerite, area tapers posteriorly to form a
subtriangular apical projection of distal arm sclerite, bearing subdistally a simple,
curved seta; in anterior view apical projections narrowly subtriangular with a
blunt apex, high anterior expanded portion supported also by anterior, sclerotized,
J-shaped ridges on either side, small arm of “J” facing medially; area between
“J” sclerites appears to be Open as a large anterior fossa, with proximal margin
bounded by anterior arch, distal margin bounded by a membrane folding over top
of apical projections of distal arm sclerites; posterior rami not evident.
Neumania sp.
Fig. 36
This species is, in general, similar to Hydrodroma in the structure of the EC
skeleton.
PROXIMAL CHAMBER circular to oval in anterior view, oval to subrectangular
in lateral view, proximal and posterior walls moderately sclerotized, lateral walls
lightly sclerotized; anterior surface primarily membranous, supported and strength-
ened laterally and proximally by a divided anterior margin sclerite; in anterior
view each part of margin sclerite L-shaped, joined medially in proximal margin by a
ligamentous band, not fused; distolateral borders of chamber not sclerotized; lateral
walls strengthened by an oblique sclerite articulating anteroproximally with proximal
edge of anterior margin sclerite, articulating distoposteriorly with base of proximal
arm.
POSTERIOR KEEL attached to distal part of posterior surface of proximal cham-
ber, broadly attached, subrectangular in shape, rounded proximally, tapering
irregularly distally to a short, strong, sclerotized distal rod; distal rod free
from body of EC throughout, merging gradually with distal membranes at level
of anterior keel.
PROXIMAL ARMS long, slightly curved in anterior view, sturdy, heavily sclero-
49
Neumania sp.: a, anterior view; b, lateral view.
Neumania sp. (nr. N. distincta): a, anterior view; b, lateral view.
Oxus sp. (nr. O. connatus): a, anterior view; b, lateral view.
Oxus sp. (nr. O. intermedius): a, anterior view; b, lateral view.
tized, broadest basally, tapering gradually to an expanded apex, approximately
twice as long as proximal chamber in anterior view; chamber ramus absent; distal
rami slender, strongly sclerotized, proceeding distad to level of anterior keel;
basal plate small, subquadrate, lying in lateral wall of EC distal to base of
proximal arm.
MIDSECTION Of EC lightly sclerotized, complex in structure; in anterior view
can be seen a proximal bilobed chamber (Cmb 1), a distal, axillary, rounded
chamber (Cmb 2), and posterior and lateral to these two, an elongate, sac-like
chamber (Cmb 3); in anterior view, a pair of short, heavy, laterally placed, dumb-
bell-shaped sclerites (PrxSc 1), anterior expanson of each sculptured for muscle
attachment.
ANTERIOR KEEL high, narrow, slightly curved (convex distally) oval, apex acute,
lateral surfaces heavily sculptured for muscle attachment, base broad but not
tapering distally beneath anterior arch.
DISTAL ARM strong, heavily sclerotized, wide basally, tapering regularly to an
acute apex, curved in anterior view, apex only slightly expanded; anterior ramus
high, broad basally, tapering to sharp, acute apex, apices of either side apposed on
median line; distal arm joined to lateral wall of EC by a strongly sclerotized rod
that is expanded medially into a subtriangular plate, broadly attached to lateral
surface of lobe-shaped lateral chamber, probably representing a modified lateral
shelf; no apical setae observed.
Neumania sp.
(nr. N. distincta) Fig. 37
The EC of this species differs from that of the previously described Neumania sp.
in being somewhat larger and more heavily sclerotized. Stout, proximal ramus
produced medially from anterior margin sclerite, bearing apically a pair of short,
truncate, proximal horns; no lateral wall sclerite strengthening proximal chamber;
posterior keel large and subtriangular; distal rod of normal length; midsection of
EC elaborated into four pairs of lightly sclerotized lateral chambers (Cmb 1-4)
and one short, twisted, spindle-shaped sclerite (PrxSc 1); all rami and projections
of distal arm sclerite larger and stronger; a pair of short, stout, apical setae
present.
Oxus sp.
(nr. O. connatus) Fig. 38
This species shows a great reduction of size and complexity of sclerotized EC
Structures as compared with Hydrodroma.
: PROXIMAL CHAMBER narrowly oval, elongate in anterior view, in lateral view
high, broad, subrhomboid proximal and posterior walls moderately sclerotized
lateral walls lightly sclerotized, anterior wall largely membranous; lateral sind
proximal margins of anterior surface supported by a narrow, U-shaped margin
sclerite, distal tips proceeding posteriorly at distal edge of proximal chamber
forming a shoulder and sclerotized distolateral border of chamber, fusing then with
lateral sclerotized surfaces of EC and basal plate of proximal arm sclerite; lateral
wall sclerite absent; no trace of proximal horns.
POSTERIOR KEEL rudimentary; a thin, narrow, lightly sclerotized distal rod
appears to arise directly from posterior side of proximal chamber, proceeds for-
ward curving slightly in a sinuate fashion not far from posterior surface of EC
but not fused with it.
Dil
PROXIMAL ARM a short, hollow, subconical structure, roughly triangular in
anterior view, in lateral view expanded anteroposteriorly, surface lightly sculptured
for muscle insertion; chamber ramus not recognizable; distal rami proceed distad
in an approximately lateral position parallel with lateral walls of EC to midway
along length of distal arm sclerites; basal plate large, subtriangular, lying partially
distal to proximal chamber in walls of midsection of EC, strengthened by three
sclerotized struts, two proceeding from base of proximal arm, third lying in a
central position on plate, proximal portion expanded into a thin, triangular plate in
lateral walls of proximal chamber.
MIDSECTION Of EC lightly sclerotized, relatively simple in structure; inflated
in anterior view (Cmb 1), high in lateral view.
ANTERIOR KEEL narrow and elongate; obliquely placed in lateral view, lying
along distal portion of anterior margin of midsection of EC; high at proximal end,
sloping down distally to level of distal arm sclerites.
DISTAL ARM sSclerites greatly expanded, fused and modified to form a lightly
sclerotized, apical cone at distal end of EC; cone thin, membranous anteriorly,
proximal margins moderately well sclerotized; no setae observed on this sclerite.
Oxus sp.
(nr. O. intermedius) Fig. 39
The EC of this species shows great modification of the Hydrodroma pattern and is
altered as well from that previously described for Oxus sp. (nr. O. connatus).
Proximal chamber greatly enlarged in lateral view but narrow in anterior view;
anterior surface greatly elongated proximally, curving clockwise through 180°;
distal tips of anterior margin sclerite produced posteriorly forming strong, sub-
triangular, distolateral border sclerites; two short, tapering, sclerotized ridges lie
side-by-side in membranes of anterior surface at distal border of chamber, each
giving rise to a short, subconical, blunt anterior horn; posterior keel and distal rod
absent; proximal arm short, blunt, fused basally with distolateral border sclerite;
basal plate produced posteriorly as a narrow, sinuate, strap-like sclerite further
strengthening distolateral border of proximal chamber; midsection and distal region
lightly sclerotized, inflated to form an irregular chamber (Cmb 1); distal arm
sclerites reduced to sclerotized thickenings in walls of Cmb 1.
Piona pinguipal pis
Fig. 40
The EC of this species differs from that of Hydrodroma primarily in the remarkable
development of the proximal chamber. Determined from Cook, 1960.
PROXIMAL CHAMBER greatly elongated, narrowly oval in anterior view, in lateral
view subrectangular, long, low; unusual feature of proximal chamber is extension of
posterior wall and of anterior surface into a curving, helical, proximal projection,
an elongate, blunt, narrow, blind sac appended proximally to proximal chamber;
lateral, posterior, and rest of proximal surfaces all more nearly normal, moderately
sclerotized, lateral surfaces not strengthened by sclerites; anterior surface primarily
membranous, elongate, forming anterior surface of proximal sac; anterior margin
sclerite approximately normal in shape, in anterior view elongate, narrow, U-shaped,
wide proximally, tapering distally on either side, proximal section of sclerite raised
anteriorly, arched over anterior surface of chamber so that anterior surface pro-
ceeds beneath its proximal end, being attached to it by membranes and is then
produced proximally into blind sac; proximal horns absent.
DZ
POSTERIOR KEEL hatchet-shaped, connected to posterior surface of proximal
chamber by a thin, oblique stalk, broadening posteriorly into an obliquely placed,
subrectangular plate, truncate proximally, tapering distally to give rise to a
moderately well-sclerotized, evenly curved (convex posteriorly) distal rod; distal
rod free from posterior surface of EC throughout most of its length, although
closely applied to posterior surface.
PROXIMAL ARMS broad, strongly curved in anterior view, widest at shoulder,
tapering basally and apically, proximal apex acute, blunt, lateral margins much
expanded to form a thin, sculptured plate for muscle insertion; basal plate small,
lying distal to base of proximal arm in lateral wall of midsection of EC; distal
ramus strong, heavily sclerotized; chamber ramus absent.
MIDSECTION of EC in part lightly sclerotized, in part membranous; in lateral
view most of area occupied by basal plate of proximal arm sclerite, by a T-sclerite
(DisSc 1), linear in lateral view, and by an anterolateral chamber (Cmb 1), more
fully visible in anterior view; in anterior view Cmb 1 lies above base of proximal
arm, subtriangular, broad lateroproximally, tapering distomedially; a pair of short,
curved sclerites (DisSc 2) subtend base of anterior keel on either side.
ANTERIOR KEEL Subtriangular with a broad base and a tall, anteriorly produced
apex that is slightly expanded and sculptured for muscle insertion.
DISTAL ARMS in anterior view narrow, well-sclerotized, strongly curved, basal
and apical portions directed at approximately 90° to one another, tapering gradually
to a truncate, slightly expanded apex; anterior rami high, broad basally, tapering
rapidly to an acute apex, apices of either side apposed on median line; area
distal to anterior ramus and distal arms expanded, produced into a thin, lightly
sclerotized, subconical structure on either side; lateral! shelf aids in formation of
posterior side of this apical development, joins base of distal arm to latera! wall
of EC; posterior rami short, blunt, subtriangular; no apical setae present.
Protzia sp.
Fig. 41
The EC of this species is unusual in that much of the lateral surface is covered by
_ folds of membranous chitin. Otherwise, the general structure is similar to that of
Hydrodroma.
PROXIMAL CHAMBER large, subrectangular in both anterior and lateral views,
proximal, posterior, and lateral walls lightly sclerotized, anterior surface largely
membranous, lateral margins of anterior surface not strengthened by sclerotized
rods, proximal margin supported and strengthened by a margin sclerite, produced
proximally on midline into a low, blunt, cone-shaped proximal ramus; lateral
wall supported in part by an oblique sclerotized rod that is broader proximo-
anteriorly at articulation with anterior margin sclerite, tapering distoposteriorly to a
blunt apex at base of proximal arm; proximal horns absent.
POSTERIOR KEEL large, subquadrate, attached broadly to posterior surface of
proximal chamber, margins irregular, produced anteriorly into a short, triangular
section giving rise to a curved, partially membranous distal rod; distal rod
short, merging at level of proximal margin of anterior keel with distal membranes
attached to posterior surface of EC.
PROXIMAL ARMS strong, heavy, well sclerotized, tapering gradually to blunt
apices; chamber ramus short, almost indistinguishable; distal ramus long, well
sclerotized; basal plate subtriangular, lying in lateral wall of EC distal to base of
proximal arm and distal in large part to proximal chamber.
MIDSECTION Of EC lightly sclerotized; only prominent sclerites in this region a
be
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L quid
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lateral view.
a, anterior view; b, lateral view.
,
Fig. 40 Piona pinguipalpis: a, anterior view; b
Fig. 41
Protzia sp.:
Pseudohydryphantes sp.:
Fig. 43 Sperchon sp.:
a, anterior view; b, lateral view.
a, anterior view; b, lateral view.
Fig. 42
54
pair of long, narrow, sinuate rods (PrxSc 1) lying in submedian position On anterior
surface next to base of anterior keel, proceeding proximad to edge of anterior
surface of proximal chamber, in lateral view wide, sides subparallel, proximal apex
expanded into a subtriangular plate; a well-sclerotized chamber (Cmb 1) present on
either side in a subaxillary position.
ANTERIOR KEEL elongate, low, subrectangular, slightly curved in lateral view,
lying obliquely, anterior margin facing anterodistally; anterior margin sinuate, ex-
cavated in distal portion to form a short, triangular projection at either end of
excavation, well sclerotized, subtended by folds of membrane.
DISTAL ARMS short, almost straight in anterior view, sides subparallel, tapering
rapidly to a blunt apex; anterior rami elongate, broad, heavy, well sclerotized,
sinuate, tapering to an acute apex in lateral view, apices apposed on midline; area
distal to anterior ramus and distal arms expanded, produced distally into a thin-
walled, cone-shaped apical structure on either side, blunt apically, bearing a strong,
straight, subapical, simple seta; posterior rami short, strong.
Pseudohydryphantes sp.
Fig. 42
The EC of this species represents an elaboration of the basic Hydrodroma plan.
PROXIMAL CHAMBER Oval to round in anterior view, subrectangular in lateral
view, lateral, proximal, and posterior walls heavily sclerotized, anterior wall pri-
marily membranous; anterior surface strengthened laterally and proximally by a
broadly rounded, U-shaped margin sclerite, thicker proximally, produced on mid-
line proximally into a short, rectangular, truncate proximal ramus appearing as a
thin plate in lateral view; distal ends of anterior margin sclerite curved posteriorly
forming a rounded shoulder, then swept posteriorly forming a sclerotized disto-
lateral border of proximal chamber, and distally as a broad, crescent-shaped
sclerite lying in lateral wall of midsection of EC; distal section of this sclerite
closely associated with elongate base of proximal arm; no strengthening sclerites
in lateral walls of proximal chamber; proximal horns absent.
POSTERIOR KEEL subtriangular, low, posterior apex rounded, base broadly at-
tached to posterior surface of proximal chamber, distal margin gives rise to a
gently curving, well-sclerotized distal rod; distal rod free from posterior surface of
EC throughout its entire length, merging gradually with membranes at level of
distal half of anterior keel.
PROXIMAL ARMS short, not strongly curved, broadest basally, tapering gradually
to a slightly expanded, blunt apex, projecting proximally about as far as apex of
proximal chamber; in lateral view proximal arms thin, sinuate, base placed far
distad on lateral wall of EC; distal ramus long, sharply pointed, ending distal to
anterior arch; chamber ramus directed proximally from base, curved, parallelling
distal extension of anterior margin sclerite; basal plate little developed, small,
triangular, lying in posterior area of lateral wall of midsection.
MIDSECTION Of EC lightly sclerotized laterally, some membranous areas ante-
riorly; strong, narrow, sclerotized ridge (PrxSc 1) lies obliquely in lateral wall,
articulating posteriorly and distally with posterior ramus of distal arm _ sclerite,
then proceeding anteroproximad, ending at proximal end of basal margin of anterior
keel; a second strong sclerite in lateral walls is a narrow, curved, elongate rod
(DisSc 1) subtending base of anterior keel; in anterior view, sclerites and pro-
jections of lateral wall define and support lateral and posterior walls of two
pairs of large lateral chambers (Cmb 1, 2), anterior walls of these chambers
appear largely membranous; two spindle-shaped sclerites (PrxSc 2) lie submedially
in anterior wall between distal margin of proximal chamber and proximal margin
of anterior keel.
52
ANTERIOR KEEL subtriangular, high, rounded anteriorly and proximally, tapering
distally to continue forward beneath anterior arch.
DISTAL ARMS short, curved in anterior and lateral views, broad basally, tapering
to an acute, blunt apex; anterior rami short, blunt, subtriangular in anterior and
lateral views; a well-developed lateral shelf present; area distal to anterior rami and
distal arms expanded, produced to form a lightly sclerotized, cone-like structure:
posterior ramus present, short, curved, tapering to an acute apex proximally: each
apical cone bearing a short, stout, curved seta subapically.
Sperchon sp.
Fig. 43
The EC of this species is greatly modified from the Hydrodroma type. The body
of the organ is composed of a long, inflated, lightly sclerotized sack consisting
primarily of the proximal chamber and the inflated midregion. The typical sclerites
are reduced and lie in the lateral walls of the structure.
PROXIMAL CHAMBER large, Oval in anterior view, rounded in lateral view, pos-
terior and lateral sides lightly sclerotized, anterior surface largely membranous; an
oblique, lightly sclerotized band lies in anterior portion of lateral wall of proximal
chamber; anterior margin sclerite U-shaped, thin in anterior view, broader and
strap-like in lateral view, distal ends proceed posteriorly as a sclerotized, disto-
lateral border of chamber, then distally as an oblique arm across lateral surface of
midsection; small proximal horns, in anterior view, project laterally, apparently as
continuations of sclerotized plate strengthening proximal surface of chamber.
POSTERIOR KEEL almost non-existent; distal rod produced directly from posterior
surface of proximal chamber, curved slightly (convex posteriorly), following poste-
rior surface of EC closely although not attached to it throughout most of its
length, distally rod becomes completely fused with posterior surface at level of
distal arm sclerites.
PROXIMAL ARM Sclerites small, simple in anterior view; arms short, slightly
curved, broad basally, tapering regularly to a blunt apex; only well-developed ramus
is chamber ramus proceeding obliquely from base of proximal arm antero-
proximad to fuse-with distal end of anterior margin sclerite.
MIDSECTION of EC large, approximately diamond-shaped in lateral view,
anterior and lateral walls lightly sclerotized, anterior surface high, arched ante-
riorly, lateral walls expanded to form large axillary chamber (Cmb 1) on either
side; a longitudinal median chamber (Cmb 2) subtends anterior keel; Cmb 1
strengthened by one oblique sclerite (DisSc 1) in distal half of lateral wall, tapering
posterodistally, articulating with base of distal arm sclerites; a number of sclerotic
ridges give additional support to lateral walls.
ANTERIOR KEEL low, elongate in lateral view, slightly curved (convex ante-
riorly), perched upon anterior surface of Cmb 2.
DISTAL ARM sclerites much reduced, distal arms short, slightly curved, tapering
to a blunt apex; anterior rami directed distad, long, thin, curving almost to midline
over anterior surface; posterior ramus indistinct, probably fused with DisSc 1; a
semi-membranous, curved rod projects posteriorly, on either side, from posterior
surface at level of distal arm (cf. posterior ramus in Hydryphantes); no apical
development or apical setae.
56
Sperchonopsis sp.
Fig. 44
The chitinized EC skeleton of this species is similar to that of the Sperchon species
just described. It differs primarily in being proportionally higher (anterior to
posterior direction), more heavily sclerotized, and more elaborate. Proximal
chamber larger, subquadrate in lateral view; proximal horns thin, lightly sclerotized,
elongate; basal plate of proximal arm sclerite large, aiding in formation of a lateral
over-hanging wall in midsection; lateral walls of axillary chambers (Cmb 1) well
sclerotized; DisSc 1 broad, curved and strap-like; each distal arm sclerite giving
rise to a cone-like apical development that curves posteriorly and bears subdistally
a short, stout, apical seta; posterior ramus of distal arm sclerite evident.
Testudacarus sp.
Fig. 45
The EC of this species is a compact, moderately sclerotized structure, easily
referable to the basic Hydrodroma type.
PROXIMAL CHAMBER large, subcircular in anterior view, subrectangular in
lateral view; lateral, proximal and posterior walls moderately sclerotized; anterior
portion of chamber more rounded, posterior portion narrower, more trough-like;
anterior surface primarily membranous, supported and strengthened laterally and
proximally by a margin sclerite; margin sclerite rounded, broadly V-shaped in
anterior view, distal tips forming a shoulder at anterodistal corner of chamber,
then proceeding obliquely posterodistad, finally curving distad across surface of
lateral wall of midsection; margin sclerite produced proximally into a short, blunt,
rounded proximal ramus, and laterally on either side to form a thin, tapering,
lightly sclerotized proximal horn; lateral walls of proximal chamber strengthened
and supported by a sinuate oblique sclerite.
POSTERIOR KEEL a short, low ridge, tapering distally and proximally, slightly
curved (convex posteriorly), applied to posterior surface of proximal chamber near
distal border of chamber; distal rod absent.
PROXIMAL ARMS short, strong, almost straight in anterior view, widest basally,
tapering gradually to a slightly expanded, sculptured apex, reaching proximally only
about half as far from their base as apex of proximal chamber; chamber ramus
short, strong, fused with distal section of anterior margin sclerite where it travels
across lateral surface of EC; distal rami curve posterad, then strongly anterad and
distad; basal plate roughly triangular, lying wholly in lateral wall of EC distal to
base of proximal arm, almost entirely covered by sclerotized flaps or chambers
elaborated in lightly sclerotized wall.
MIDSECTION Of EC moderately sclerotized, elaborated into a number of plates,
chambers, and sclerotized structures, entire area large, subrectangular in anterior
and lateral views; treating first structures of anterior surface, proximal-most anterior
sclerite (PrxSc 1) horseshoe-shaped (concave distally), lying on midline just distal
to anterior surface of proximal chamber, forming an anterior margin for this
area; distal-most anterior surface sclerite (DisSc 1) in form of a long, narrow,
U-shaped structure with sub-median ramus on either side elongate, narrow, tapering,
sinuate, rami on either side joining on midline just proximal to base of anterior
keel; both PrxSc 1 and DisSc 1 broad, plate-like in lateral view; lateral surface of
midsection with a number of sclerotic surface ridges, folds, plates and some folded
membranous areas posteriorly; most prominent feature, a subtriangular lateral
chamber (Cmb 1) axillary to distal arms; walls of this chamber strengthened by a
V-shaped (in anterior view) sclerite (DisSc 2), apex projecting laterally, arms fused
basally with lateral walls of midsection.
a7
pdy
wyuy
re)
a, anterior view; 5, lateral view.
Fig. 44 Sperchonopsis sp.:
, anterior view; b, lateral view.
Fig. 45 Testudacarus sp.: a
b, lateral view.
, anterior view; 5, lateral view.
?
: a, anterior view;
Fig. 46 Thyas barbigera
Fig. 47. Tiphys sp. (nr. T. americana): a
58
ANTERIOR KEEL triangular in lateral view, broadly joined to anterior surface of
area delimited by DisSc 1 and elevated on this structure, anterior margin almost
straight, irregular, with a thin, finger-like proximal extension; proximal margin
strongly concave.
DISTAL ARMS short, straight, tapering gradually to a blunt apex, apices sculptured
slightly for muscle attachment; anterior ramus lacking entirely; posterior ramus
forms part of lateral chamber (Cmb 1); area distal to base of distal arm expanded,
produced to form an elongate, narrow, blunt, cone-like apical development, each
cone bearing a short, curved, simple seta subapically.
Thyas barbigera
Fig. 46
The EC of this species is robust and heavily sclerotized but displays a tendency to
reduction of the distal arm sclerites. Determined from Cook, 1959.
PROXIMAL CHAMBER Subquadrate in anterior view, subrectangular in lateral
view, lateral, proximal, and posterior walls lightly sclerotized; anterior surface
primarily membranous; in lateral view, anterior margin sclerite forms a pronounced
anterodistal shoulder to proximal chamber and distal tip of sclerite, then pro-
ceeds posterad and distad in a broad arc onto lateral surface of midsection of EC,
in anterior view this broad crescentic sclerite narrow, entirely free from lateral
surface of midsection; anterior portion of lateral chamber wall strengthened and
supported by a curved, strongly sclerotized, oblique, rod-like wall sclerite; anterior
margin sclerite produced proximally on midline into a short, subrectangular proximal
ramus, truncate in anterior view.
POSTERIOR KEEL elongate, narrow, suboval, attached by a short, broad stalk to
posterior surface of proximal chamber, proximal margin rounded, distal margin
irregular, tapering to give rise to short, almost straight, distal rod; distal rod
becomes indistinct just proximal to level of distal arm sclerites, fused at this point
with portions of distal membranes.
PROXIMAL ARM massive, strongly curved, broadest basally, tapering gradually to
slightly expanded apex, reaching proximad to about apex of proximal chamber;
chamber ramus fused with sclerotized distolateral border of chamber and with
lateral wall sclerite; distal ramus heavy, elongate, well sclerotized, strengthening
posterior and lateral walls of midsection; basal plate small, broadly fused with
distal section of anterior margin sclerite.
MIDSECTION Of EC moderately well sclerotized; main feature of the region a
subaxillary lateral chamber (Cmb 1) with sclerotized walls, subtending anterior
keel; supported laterally by a strong, V-shaped sclerite (DisSc 1); a high, thin,
membranous, median chamber (Cmb 2) lies proximally on anterior surface, ex-
tending part way over proximal chamber.
ANTERIOR KEEL elongate, slightly expanded distally, apex rounded.
DISTAL ARMS elongate, thin, well sclerotized, in anterior view almost straight,
slightly curved near apices, broad basally, tapering apically; anterior rami short,
massive, subtriangular in lateral view, subquadrate in anterior view, apices apposed
medially; area distal to anterior ramus and distal arms expanded to form a short,
blunt, cone-shaped apical development on either side bearing a simple apical seta
subdistally; posterior rami short, but strong; a small, subtriangular, lateral shelf
joins base of distal arm to lateral surface of EC.
59
Tiphys sp.
(nr. T. americana) Fig. 47
This species possesses an EC of the generalized Hydrodroma type, with a pronoun-
ced elongation of the proximal chamber.
PROXIMAL CHAMBER long, narrowly oval in anterior view, subrectangular in
lateral view; lateral and proximal surfaces lightly sclerotized, posterior surface
more heavily sclerotized; anterior surface membranous, membrane thick and
leathery in appearance: lateral and proximal margins of anterior surface supported
by a long, narrow, U-shaped margin sclerite, arms subequal in width throughout
their length, apices expanded, round, blunt; proximally, anterior margin sclerite
gives rise to two long, stout proximal horns directed distolaterad, each with its
base on midline, each possessing an expanded, sculptured apex for muscle attachment.
POSTERIOR KEEL an elongate, strap-like sclerite, produced and rounded proxi-
mally, broadly attached to posterior surface of proximal chamber, tapering distally
to form a long narrow, well-sclerotized distal rod: distal rod only slightly curved,
parallelling posterior surface of EC beyond distal arm sclerites, free from EC,
merging with distal membranes at level of distal arms.
PROXIMAL ARMS short, broad basally, tapering to a narrow region subapically,
apex expanded into an almost circular sculptured knob; chamber rami absent;
distal rami strong, well sclerotized, proceeding forward to level of anterior keel;
basal plate elongate, spindle-shaped in lateral view, lying two-thirds in lateral
wall of proximal chamber, one-third in lateral wall of midsection of EC,
strengthened by several strongly sclerotized struts from base of proximal arm.
MIDSECTION of EC lightly sclerotized, walls produced into four small, lobe-
like chambers on either side and one small, sclerotized median chamber anteriorly,
beneath over-hanging proximal section of anterior keel.
ANTERIOR KEEL an elongate subrectangular plate, obliquely placed; broader
basal end fused distally with anterior surface of EC, keel then projects antero-
proximally, over-hanging proximal portion of anterior surface; apex irregular, tip
acuminate.
DISTAL ARMS slender, tapering from a broad base gradually to a narrow, blunt
apex, only slightly curved in anterior and lateral views; anterior ramus a strong,
short rod in lateral view, tapering to blunt apex, subtriangular in anterior view;
apices and medial margins apposed on midline; lateral shelf apparently absent;
apical setae absent.
Torrenticola sp.
(designated species A) Fig. 48
The EC of this species is much modified from the Hydrodroma type. Both
structural complexity and degree of sclerotization are reduced.
PROXIMAL CHAMBER elongate, Oval in anterior view, subrectangular in lateral
view; lateral, posterior, and proximal surfaces lightly sclerotized; anterior surface
primarily membranous, supported laterally and proximally by a U-shaped margin
sclerite; margin sclerite thin, of approximately uniform width, directed posterad at
distal margin of anterior surface to form an anterodistal shoulder to proximal
chamber, not proceeding far in lateral wall; upper surface of lateral wall of
proximal chamber strengthened by an oblique, narrow, rod-like sclerite; proximal
portion of anterior margin sclerite gives rise laterally on either side to a short, blunt
proximal horn.
60
POSTERIOR KEEL small, subtriangular, attached to distal portion of posterior
surface of proximal chamber, tapered apically to give rise to a slightly curved,
moderately sclerotized distal rod, separated from body of EC throughout most
of its length, fused with it again distally.
PROXIMAL ARMS Short, blunt distally, apical and basal areas slightly expanded;
chamber ramus and basal plate rudimentary; distal ramus proceeds posteriorly and
distally in lateral wall of proximal chamber, fused at its distal tip with a sclerite
(PrxSc 1) lying in posterolateral section of midpart of EC.
MIDSECTION of EC lightly sclerotized, simple; general configuration that of a
tube, wider proximally, tapering slightly distal to level of distal arm sclerites;
an approximately heart-shaped, membranous region delimited medially in proxi-
mal half of anterior surface; lightly sclerotized areas distal and lateral to this;
strong rod-shaped sclerite (PrxSc 1) lies in posterior region of each lateral wall,
with a small lateral arm projecting laterally on each side, one-third of distance
from proximal end.
ANTERIOR KEEL elongate, low, anterior margin gently concave, distal margin
convex, rounded, distal and anterior borders strengthened by a sclerotized thickening.
DISTAL ARMS thin, moderately well-sclerotized in anterior view, swept back,
slightly concave laterally, apices narrow, simple; in lateral view arm subtriangular,
wing-shaped, lateral and proximal margins strengthened by sclerotized thickenings;
anterior ramus absent, only bases of distal arms apposed on midline; area of
distal arm sclerites distal to base produced into an apical development forming a
single, subconical structure; apical cone low, blunt, rounded distally; other rami of
distal arm sclerites absent; apical setae absent.
Torrenticola sp.
(designated species B) Fig. 49
The EC of this species is greatly elongated and apparently modified for internal
insemination. Proximal chamber small, oval, anteroposteriorly compressed, lightly
sclerotized; proximal horns absent; distolateral border and anterodistal corner of
chamber sclerotized; posterior keel elongate, linear; distal rod absent: distal ramus
of proximal arm sclerite strong, heavily sclerotized; midsection short, lightly sclero-
tized; a broadly U-shaped anterior sclerite (PrxSc 1) in this section forms a distal
margin to proximal chamber, gives rise on either side to a short, lateroposteriorly
directed rod (PrxSc 2) strengthening lateral wall of lateral chamber (Cmb 1); ante-
rior keel elongate, linear, membranous; distal arm sclerites strongly modified, con-
sisting Of a proximally directed distal arm extending to edge of proximal chamber
and a greatly elongated, cylindrical apical development, blunt distally; each apical
development bearing a long, simple, subdistal seta; posterior surface of EC also
produced distad to form a shallow, lightly sclerotized trough partially supporting
apical developments of distal arm sclerites.
Tyrrellia sp.
Fig. 50
The EC of this species is unusual and unlike any other that I studied. It is appa-
rently strongly modified in response to some particular element of the mite’s habits
or habitat, for instance, the necessity of accomplishing insemination in a water-
film environment. Structures can be compared only with difficulty with those of
Hydrodroma, but the strong resemblance of the adult to the typical water mites
justifies the following unsatisfactory attempt. The final elucidation of this organ
awaits an intensive study of its functional morphology and of the behaviour and
61
/ =f
L2SX4q ——— pUNN tA
ZzIDA A
Z 2$X4d aver
(
pivy
L 2S*4d
wy Xid
Z 2SX4d
PSM
L2Sx4d
wy Xid
ee,
view.
Fig. 49 Torrenticola sp. B: a, anterior view; b, lateral view.
Fig. 48 Torrenticola sp. A: a, anterior view; b, lateral
a, anterior view; b, lateral view.
Fig. 50 Tyrrellia sp.:
a, anterior view; b, lateral view.
Unionicola sp.:
Fig. Sf
62
life history of the species. In the body of the adult male, the EC projects ventro-
posterad into the phallocrypt so that the surface designated anterior in Hydrodroma
faces ventrally. This is the surface illustrated in Fig. 50a. Sclerites are lettered
(A-D) because of their uncertain homology.
Proximally, a capacious, lightly sclerotized (proximal ?) chamber surrounds
the basal half of the organ. The paired sclerites (A) on the anterior surface
may be homologous with the proximal arm sclerites of Hydrodroma or, in part,
with the anterior margin sclerite. The conspicuous, broad, flat distal plates (D)
bear a strong, anteriorly-directed spine at the mediodistal corner, and the lateral
edges are toothed. These sclerites are probably homologous with some elements of
the distal arm sclerites of Hydrodroma, but appear to serve a special function in
Tyrrellia. The presence of a band of muscles joining a posterior projection (C)
from these plates with a median posterior projection (B) suggests that the distal
toothed plates (D) can be moved scissor-like, in the horizontal plane. This may
be linked with an unusual method of spermatophore deposition. “The triangular
plate lying proximal and anterior to the EC and joined to it only by membrane is
apparently the median anterior sclerite in the genital field of the ventral body wall.
It appears to function as a point of anchorage for the EC.
Unionicola sp.
Fig. 51
The EC of this species is an elaboration of the basic Hydrodroma type. The organ
is robust, complex, and heavily sclerotized.
PROXIMAL CHAMBER Subquadrate in anterior view, subrectangular to oval in
lateral view, lateral, posterior, and proximal surfaces moderately sclerotized, anterior
surface primarily membranous; margins of anterior surface supported and strength-
ened only proximally by a wide, curved proximal sclerite, lateral arms of this
sclerite absent; an oblique sclerite present in anterior portion of lateral wall,
roughly L-shaped (convex posteriorly), short arm articulating anteroproximally with
proximal section of anterior margin sclerite, tapering distal tip articulated and
partially fused with base of proximal arm; anterior margin sclerite produced proxi-
mally on midline into a short, broad proximal ramus, subrectangular in anterior
view, a short, stout rod in lateral view; from either proximal corner of proximal
ramus is produced a stout, well-sclerotized, L-shaped, proximal horn, short limb
of “L” fused with proximal arm, directed proximolaterally, long arm of “L”
directed posteriorly, sinuate, tapering to a blunt apex.
POSTERIOR KEEL suboval, attached to distal portion of posterior wall by a short,
narrow stalk, posterodistal corner of keel produced into a sinuate, strongly sclero-
tized distal rod; distal rod well separated from posterior surface of EC throughout
its entire length, fusing with distal membranes and walls of sperm passage only
distal to distal arm sclerites.
PROXIMAL ARMS long, stout, broad in anterior view, hardly tapering, expanded
into a subtriangular apex, unusual in giving rise basally to a postetriorly directed arm
ramus; arm ramus short, stout, tapering slightly, truncate apically, bearing a small
apical projection possibly a tendon for muscle or membrane attachment: chamber
ramus absent; distal rami short and stout.
MIDSECTION Of EC lightly sclerotized; area characterized by a number of
chambers or outpocketings both laterally and anteriorly, and by a pair of prominent
T-shaped sclerites (PrxSc 1); in lateral view PrxSc 1 seen to have a complex struc-
ture consisting of a horizontal sclerite, broadly rounded distally, also rounded
and narrower proximally, bearing two anteriorly directed, curved, thin rami; loca-
tion of chambers follows: Cmb ‘1, in proximal section of lateral wall overlapping
63
anterodistal section of lateral surface of proximal chamber; Cmb 2 medially placed
on anterior surface of midsection, subtending proximal end of base of anterior
keel; Cmb 3, posteriorly in lateral wall directly below base of anterior keel;
anterior surface also bears a small pair of sclerites (PrxSc 2) lying submedially,
proximal to base of anterior keel in membranous area of anterior surface.
ANTERIOR KEEL high, crescent-shaped (convex distally), apex bluntly rounded.
DISTAL ARM sclerites massive, broadly expanded, heavily sculptured; distal arms
short, almost straight, thin in lateral view, broad in anterior view because of
medial, shelf-like expansions; anterior ramus elongate, narrow, tapering from a
broad base to a small, blunt apex; lateral shelf greatly expanded, produced proxi-
mally near body of EC thus forming a broad connection between distal arm and
lateral surface of midsection; this shelf also produced posteriorly as seen in lateral
view, in concert with posterior ramus, forms a posterior wing-like projection beside
lateral surface of EC, this extension then joined to lateral wall by a fold of
membrane near base of proximal arm; lateral shelf divided so that distal arm
also joined to lateral wall by a short, stout, well-sclerotized rod; entire sperm
passage produced distal to these sclerites forming a lightly sclerotized tube, narrow
in lateral view, somewhat oval in anterior view.
Assessment and Analysis of Similarities
HOMOLOGY
In the comparative morphological study of a given life history stage,
embryological evidence is rarely available. Homology can, however, be
justifiably inferred from similarity of form and of position in a well-
defined functional system. The degree of confidence placed in con-
clusions based on this ‘practical’ homology is increased when (1) there
is reasonable homogeneity of structure among the organisms studied, and
(ii) both functional and anatomical relationships of structures are clearly
understood. Conclusions are also strengthened by parallel but independent
research on other functional systems for the same group of organisms.
Such parallelism aids in exposing both misinterpretation and the con-
fusing results of evolutionary convergence.
THE GENERALIZED WATER MITE EC
The chitinous skeletal elements of the EC are surprisingly similar through-
out the water mites with only a few exceptions. The basic function in all
genera is apparently to form and deposit the spermatophore, and the
basic mode of action probably uniform. The first sclerotized section of the
sperm passage is an enlarged proximal chamber that may be large, box-
like and robust, or narrow and elongate, or inflated, membranous and
sac-like. The lightly sclerotized anterior surface, usually supported by a
U-shaped margin sclerite, is the point of entry for semen from the ductus
ejaculatorius. The remainder of the mechanism consists of a narrow, often
complex sperm passage to the exterior. The passage is surrounded by a
series of sclerites giving purchase and leverage to several pairs of muscles
that contract in concert to operate a syringe-like mechanism, compressing
the proximal chamber and expelling its contents to the exterior.
The proximal edge of the anterior margin sclerite may be unmodified
Or may give rise to a proximal ramus or a pair of proximal horns. Fre-
64
quently a narrow, shelf-like posterior keel is attached to the posterior sur-
face of the proximal chamber and is often produced distally into an
elongate distal rod that may be free or variously fused to the body of
the EC. The distal section of the proximal chamber is invariably sup-
ported on either side by a proximal arm sclerite giving rise to a laterally
directed proximal arm. Other processes of this sclerite further strengthen
the lateral walls of the chamber and midsection of the EC.
The midsection varies more than other areas of the EC in the species
observed, often being elaborated into a number of different sclerites,
projections, and chambers. A relatively constant feature of the region is
a thin, sclerotized, longitudinal anterior keel. The keel varies in shape
and degree of sclerotization but is consistent in its median position
distally on the anterior surface of the midsection. The distal apex of the
EC is provided with a pair of distal arm sclerites that may be greatly
reduced but always persist in the form of some rudimentary sclerotization.
When well developed, each bears a laterally directed distal arm and an
anteromedially directed anterior ramus, the tips of the anterior rami
apposed on the midline to form an anterior arch. Other processes of the
distal arm sclerite strengthen the lateral and posterior walls of the mid-
section. In many species, these sclerites are expanded and developed
apically and may bear a pair of simple, apical setae. Membranes are
always inserted at some point on the distal half of the EC and attach it to
the borders of the genital opening.
SIMILARITY GROUPINGS
With the data presented it is possible to assess the similarity of the
chitinous skeleton of the EC from genus to genus and to present the
results graphically as in Figures 52-55. Feltria is omitted from this
analysis because of the lack of detailed morphological data. The figures
illustrate similarity relationships only; the length of the line joining two
taxa is inversely proportional to the degree of mutual similarity shown by
the ejaculatory complexes of the taxa, with dotted lines indicating situa-
tions in which the precise relationship is based on only one or a few
characters, and is tentative. There is no intent to illustrate phylogenetic
relationships.
Group 1 of Fig. 52 is composed of the two genera, Protzia and Hydro-
droma, showing a generalized structure of the EC skeleton. The two
have in common relatively strong, well-developed distal and proximal arm
sclerites, a pair of sclerotized lateral chambers, a well-developed disto-
lateral border to the proximal chamber, lateral wall sclerites, and a weak,
partially membranous distal rod. Protzia is similar to Limnesia in the
form of distal arm sclerites, large, robust proximal chamber, and shape of
distolateral border of proximal chamber. The latter relation indicates
that the Group 1 genera show closest affinity with those of Group 3.
Group 2 is also composed of two genera, Eylais and Limnochares, that
are characterized by a highly-modified EC. They are similar in the
reduction of the distal arms, in the configuration of the proximal arm
sclerites, with a great enlargement of the medial ramus, and in the un-
65
| cp
e
a
a
a
a
a
a
a
a
Mideopsis
Hydro -
volzia
Fig. 52 Similarity relationships based on the morphology of the ejaculatory com-
plex.
usual, arched structure formed on either side by the bases of the distal
arm sclerites. Although the basic affinity of the Group 2 genera with
other water mites is strong, the precise relationship is not clearly indicated
by the structure of the EC. But the joining of proximal and distal arm
sclerites by sclerotized struts, and the reduction of the distal arms may
indicate some similarity to Group 3 (especially Hydrachna).
Group 3 consists of 11 genera and is a large and reasonably homo-
geneous group with a complex internal structure (Fig. 53). Lebertia
occupies a central position in the similarity diagram. Thyas and Hydry-
phantes form a nucleus defined by the possession of a well-developed
66
Testud = ;
Torrenticola
acarus
Sperchon Sperchon -
opsis
Frontipoda
Lebertia
Pseudohy ~
dryphantes
Fig. 53 Similarity relationships among the genera of Group 3.
distolateral border of the proximal chamber with its extension into the
lateral wall of the EC, sclerotized lateral chambers, and a slight reduction
of the distal arms. The first and last of these features indicates similarity
to Lebertia. Sperchon and Sperchonopsis are closely similar and share so
many features that their species would perhaps be considered congeneric
on the basis of EC characters alone. They are like Lebertia in having
the midsection of the EC inflated and well sclerotized. Other similarities
to Lebertia include the form of the proximal horns and the sclerite-complex
formed by the anterior margin sclerite, distolateral border, and lateral wall
sclerite of the proximal chamber. In addition, Sperchon and Sperchonopsis
67
have in common the sclerotized bands and chambers of the midsection,
the swept-back configuration of the distal arms with low anterior rami,
and the strongly elbowed proximal arms. Testudacarus is readily placed
close to Sperchon by the virtually identical, sclerotized axillary chambers,
the configuration of the distal arms, and the sclerotized distolateral
borders. The EC in the two Torrenticola spp. examined was reduced and
modified, and there is little reliable evidence to link the genus with
Testudacarus on the basis of this structure. Nonetheless, the adult exo-
skeletal morphology of these genera is virtually identical so that, by asso-
ciation, Torrenticola is also shown to have a strong affinity with Sperchon
and Sperchonopsis. The presence of one additional genus (Testudacarus)
in the study can illuminate a previously obscure relationship.
Frontipoda and Oxus possess a modified and reduced EC with a num-
ber of similar features: extreme reduction of the distal arm sclerites, similar
shape of the basal plates, inflated chambers of the midsection, and similar,
lightly sclerotized distolateral borders of the proximal chamber. The latter,
together with the reduction of the distal arms and the possession of an
inflated median chamber below the anterior keel, link the two genera to
Lebertia. Oxus sp. (nr. O. intermedius) is more modified than the species
near O. connatus and so supports the association with Lebertia to a lesser
degree. Pseudohydryphantes is a definite, although peripheral member of
Group 3. It possesses a distinct distolateral border, a sclerotized axillary
chamber, and a proximal ramus and is most similar to Thyas._ Hydrachna
shows a general similarity to the rest of Group 3 and is placed there on
the basis of over-all facies. Although it is not closely linked to any other
genus, in the reduction of the distal arm sclerites and possession of a
well-developed distolateral border it is most similar to Thyas or Lebertia.
Limnesia possesses a generalized EC skeleton and is distinct from any
of the groups established here. It does, however, have a strong distal
sclerite in a position axillary to the distal arms suggestive of that found in
Lebertia. Also, the distal end of the distolateral border projects forward
into the midsection of the EC in a manner reminiscent of the genera of
Group 3. As suggested earlier, these features indicate that Limnesia may
be intermediate between Group 1 and Group 3.
Group 4 represents seven genera (Fig. 54) forming a less closely-
related unit than those of Group 3. Unionicola and Neumania are easily
associated by the modification in each of the lateral shelf to form a sup-
porting buttress and by the presence of a lateral wall sclerite. Forelia
is similar to Neumania, especially in the formation of a buttress from
part of the lateral shelf. And, through the form of its distal arm sclerites,
its proximal horns, and free proximal lobe of the posterior keel, Forelia
appears to be related to Piona and Tiphys, linking these to Neumania as
well.
Atractides and Hygrobates comprise another well-defined nucleus within
Group 4, sharing in common the shape of the anterior keel, the presence
of a proximal ramus, and the lateral excavation of each arm of the anterior
margin sclerite. In addition, Atractides is similar to Unionicola in the
shape of the anterior keel and in the possession of a pair of laterally placed
68
Hygrobates
Atractides
Koenikea
sooo”
Unionicola Neumania
Forelia
Fig. 54 Similarity relationships among the genera of Group 4.
Y-sclerites. Piona and Tiphys are related by a similarity of overall facies,
with an elongation of the proximal chamber, similar form of proximal and
distal arms sclerites, and a narrow, oblique anterior keel. The lateral
shelf and laterally placed Y-sclerite of Piona indicate a relationship to
Atractides.
The four genera of Group 5 (Fig. 55) exhibit strong mutual affinities
but their relationship to other mites is less clear. Axonopsis and Brachy-
poda are similar in general EC structure, each characterized by a compact,
well-sclerotized skeleton of robust components. In particular, the strong,
U-shaped anterior margin sclerite, the complex midsection, and the prox-
imally-lobed posterior keel indicate the close phenetic relationship of
these genera. Aturus presents a comparable facies and is strongly linked
to Axonopsis and Brachypoda by the structure of the anterior margin scle-
rite. The Kongsbergia EC is less specialized, but the form of the anterior
margin sclerite, the posterior keel, and the complex structure of the mid-
section tie it convincingly to the other Group 5 genera. Its more gene-
ralized structure points to an additional relationship with the genera of
Group 4, and the complex basal area of the distal arm sclerite, together
with the form of the anterior margin sclerite, suggest that of the Group 4
69
Axonopsis
Aturus
Fig. 55 Similarity relationships among the genera of Group 5.
genera in this study, it is most similar to Unionicola.
Koenikea does not fit easily into any of the groups formed thus far but
seems to be intermediate between the genera of Groups 4 and 5. The
shape of the distolateral border, the elongation of the anterior ramus, and
the reduction of the posterior keel also occur in Aturus. On the other
hand, the three pairs of lateral, midsection chambers and the medially-
based proximal horns suggest a distant affinity with Neumania.
Four additional genera do not appear to fall within any one of the five
main groups, but each can be tentatively related (Fig. 52) to one or
another of them. Mideopsis shares a heavy sclerotization of the proximal
chamber and the narrow shape of the posterior keel with Axonopsis in
Group 5. Geayia in turn has the sclerotized proximal chamber and con-
figuration of the strongly fused anterior margin and lateral wall sclerites in
common with Mideopsis. The EC of Albia is similar to that of Koenikea
in the medial placement of the proximal horns, form of the posterior keel,
and elongate anterior ramus. Thus Albia also appears distantly related
to Group 5. Midea can be linked to the same group via two features
shared with Kongsbergia: a pair of elongate, curved, rod-like distal scle-
rites anteriorly in the midsection and a median, proximally-directed exten-
sion of the anterior margin sclerite (proximal ramus). Species of these
genera are hard-bodied, actively-swimming mites, and associated modifi-
sations of the EC have possibly obscured relationships.
On the basis of overall homology of the EC skeleton, the genera of
Groups 1, 2, and 3 have a strong basic affinity with those of Groups 4
and 5. The generalized, intermediate EC structure of Limnesia is at
70
present, however, our sole indicator of the probable details of intergroup
relationships between these two larger divisions. Only the investigation
of additional genera can provide the information needed to specify precise
linkages.
The remaining three genera cannot on the basis of the morphology of
the ejaculatory complex be successfully related to any of the previously
considered groups of genera. It should eventually be possible to homo-
logize the Tyrrellia EC with that of other water mites, especially since, as
Dr. David R. Cook pointed out (in lit.), the closely related genus Neo-
tyrrellia possesses a typical EC skeleton (Lundblad, 1941a: 176) of the
Hydrodroma type. The position of Tyrrellia in the similarity diagram
(Fig. 52), however, is at present uncertain. The modifications of the
EC of Arrenurus also preclude a precise linkage with the genera studied,
but its structure could be reached by progressive alteration of the fairly
generalized EC characteristic either of Group 1 or of Group 4. Hydro-
volzia possesses an EC apparently not homologous with that of typical
water mites.
Discussion
BASIC CONCLUSIONS
Perhaps the most significant finding of the present study is the evidence
that all of the genera commonly grouped by habitat as “water mites” are
related as well by the possession of an elaborate, functional system, the
ejaculatory complex. In addition, this organ is obviously homologous in
all except two genera of the group. Substantiating evidence from genera
not covered in this investigation is available in many published taxo-
nomic illustrations that, although seldom detailed, reveal the basic EC
skeletal structure to be virtually universal in “water mites”. Equally
important is the indication from published reports that similar structures
do not occur in any related families of terrestrial mites. Thus, although
many details of the inter-relationships of various water mite genera remain
unclear, a distinctive, common character complex unites them all and
separates them decisively from related terrestrial genera.
New efforts to locate the nearest relatives of water mites among the
terrestrial taxa should take the ejaculatory complex into account along
with all other available evidence. Feider’s (1959) phylogenetic specula-
tion was certainly premature, and based on the inadequate treatment in
the literature of the water mite EC.
Several important factors in water mite systematics were discovered
or confirmed. The genus in this group is indeed a homogeneous and
stable taxonomic category, and the interspecific similarity of the EC
within a single genus is great. Conversely, from observations on Arre-
nurus, Oxus, and Torrenticola, species similar in external exoskeletal mor-
phology may regularly be expected to differ in significant details of the
Structure of the EC skeleton. Thus this organ can be used as a source of
characters to provide increased resolution of species discrimination,
especially in difficult taxa.
71
The EC may provide useful information for constructing suprageneric
classifications, as many characters are common from genus to genus. One
draw-back in the use of the organ at this classificatory level is that exten-
sive modifications can obscure the affinities of a given EC type. For
instance although the strong affinity of Eylais, Limnochares, and Arrenurus
to each other and to other water mites is demonstrated, the EC gives little
evidence of the precise nature of this relationship. Such problems are
partially alleviated by the study of all available genera and of as many
species within each genus as possible. Thus, it may be possible to discover
situations transitional to each highly modified state.
IMPORTANCE FOR CLASSIFICATION
The generic coverage of the present study is not complete enough to
form the basis for a thorough reclassification of the water mites. Indeed,
it would be an unjustifiable and arbitrary procedure to base a classificatory
system upon any such limited set of characters. Nevertheless, the results
obtained raise important questions about the accepted classification and
suggest changes that warrant further study.
The most obvious point raised is the strong cohesiveness of the genera
comprising the water mites, suggesting that all families except the Hydro-
volziidae be grouped in a single superfamily, equivalent to the Hydrovol-
zioidea and the terrestrial superfamilies of the Parasitengona. In addition,
the number of families of water mites currently recognized could be
decreased to offset the past over-emphasis on the diversity of adult forms.
Relationships within the genera of Group 3 (Fig. 53) differ consider-
ably from those shown in Viets and Viets (1960, Appendix A). The
Sperchonidae and Torrenticolidae cluster strongly, whereas the Oxidae,
Lebertia and (to a lesser extent) Hydrachna are rather closer to the
Thyasidae. The Group 4 genera (Fig. 54), however, cluster in much the
same way as might be expected from the traditional classification. Only
the absence of Koentkea from this group is surprising. The Axonopsae,
Mideopsae, and Krendowskiae exhibit a greater mutual affinity than 1s
indicated by the current classification. But Group 5 and related genera
demonstrate a configuration easily predicted from Appendix A.
PHYLOGENETIC SIGNIFICANCE
The discussion above has been concerned primarily with the related
concepts of phenetic affinity and practical classification of similar or-
ganisms. Normally, such basic observations should lead to a clearer
insight into the phylogenetic history of the taxa involved. Two main
factors, however, prevent the immediate construction of satisfactory phylo-
genies for the water mites. The first is the lack of thorough cataloguing
of the diversity of taxa to be found within the group and the primitive
state of our knowledge of life histories, immature stages, behaviour, and
physiology. An additional problem is the even greater lack of published
data for those related terrestrial families from which the water mites
almost certainly evolved. It is thus difficult to establish which are
primitive and which are derived states, or to determine how many possible
72
ancestors exist within the Parasitengona.
Therefore the erection of a detailed phylogeny now is inadvisable, but
data given here suggest an important guideline. In spite of the great
diversity of adult exoskeletal morphology and of larval structure and be-
haviour, there are still good grounds for retaining the tentative hypothesis
of a monophyletic origin for the freshwater Parasitengona (excepting
Hydrovolzia).
No genus provides a convincing exception to the hypothesis of mono-
phyly. The EC of Tyrrellia is as difficult to relate to the typical water
mite structure as is that of Hydrovolzia. But Hydrovolzia is distinct in
adult and larval morphology, whereas Tyrrellia is a typical water mite in
every respect and is moreover closely related to the genus Neotyrrellia,
with normal EC structure (Lundblad, 194la: 176). Certain “lower”
genera (e.g. Eylais, Limnochares) differ considerably in EC structure
from other water mites. But so do such “higher” genera as Oxus and
Arrenurus, and no intrinsic evidence exists to suggest whether these dif-
ferences are primitive or derived. Evidence from other sources (Mitchell,
1957a) indicates that the group 3 genera, especially Thyas, may be
closest to the terrestrial ancestor. Most important, the intergeneric dif-
ferences are minor when compared to the great morphological discon-
tinuity beteween the EC of water mites and that of related terrestrial
Parasitengona.
Convergence is rejected at present as the explanation for uniformity
of basic EC structure because there are no apparent factors (environmen-
tal or otherwise) to explain the widespread similarity observed in genera
otherwise characterized by the most extreme diversity. Certainly require-
ments for sperm transfer in an aquatic habitat did not alone produce the
effect, for Hydrovolzia and other aquatic and semi-aquatic Prostigmata
have not developed in a similar manner. Parallel evolutionary develop-
ment of the EC is a more plausable hypothesis but is usually based in turn
on monophyly (Mayr, 1969: 82). For the moment, monophyly fur-
nishes the most parsimonious explanation of the simiiarities observed in
the EC of water mites.
Because of the restricted number of characters on which it is based,
the evidence at hand cannot be considered as conclusive but has sufficient
merit that the hypothesis of monophyly for all water mites (excluding
Hydrovolzia) should be retained for further scrutiny.
Summary
its
74
A comparative study of the male reproductive system was under-
taken to provide evidence pertinent to the classification of freshwater
mites.
a. The water mite genus is the most convenient comparative unit for
such a study.
b. The term ejaculatory complex (EC) is the most suitable of
several for the terminal organ in the male genital tract.
c. Present deficiencies in the specific taxonomy of North American
water mites dictate that the deme is often the only definable
category below the genus.
The water mite EC has not previously been adequately explained
either structurally or functionally.
The EC of Hydrodroma is a well-muscled, chitinous framework that
functions as a syringe-like organ for the reception, compacting, and
expulsion of masses of spermatozoa.
An analysis of EC structural similarities leads to the delimitation of
several large groups of genera showing a high degree of internal affi-
nity. These groups coincide only partially with conventional classi-
fications.
The EC is shown to have potential value for classification and phylo-
genetic speculation at every taxonomic level.
No other group of mites possesses a chitinous EC skeleton of the type
found in water mites.
The basic EC structure appears to be homologous in all water mite
genera with the exception of Hydrovolzia.
Available evidence from the EC is consistent with a monophyletic
origin for all water mite genera except Hydrovolzia.
Glossary of Morphological Terms
Terms are defined to correspond with the usage of the present report.
Thus, even familiar terms are included where their application to mites
may be unclear.
ANTERIOR: that surface of the EC usually facing in an anterodorsal direction when
the organ is in situ; the surface through which the ductus ejaculatorius enters
the EC.
ANTERIOR ARCH: the bridge-like structure formed by the apposed anterior rami
(aq. v-)’.
ANTERIOR HORN (AntHn): a short, subconical, sclerotized projection arising from
each of a pair of sclerites lying in the anterior wall of the proximal chamber
of Oxus sp. (nr. O. intermedius).
ANTERIOR KEEL (AntKI): a thin, plate-like structure usually borne medially on the
anterior surface of the EC, often roughened for muscle attachment.
ANTERIOR MARGIN SCLERITE (AMScl): a sclerotized thickening in the lateral and
proximal margins of the anterior surface of the proximal chamber.
ANTERIOR RAMUS (AntRm): an anteromedially directed rod arising from the base
of the distal arm sclerite; apices of the anterior rami of either side usually
apposed, often attached or fused on the midline.
ANTERIOR SCLEROTIZED SURFACE: anterolateral walls of midsection of Hydrodroma
EC; subtending the anterior keel.
APICAL: pertaining to the free, unattached tip of any structure, especially the distal
portion of the EC.
APICAL DEVELOPMENT (Apcl): any sclerotized elongation of the distal arm sclerites
distal to the bases of distal arms and anterior rami.
APICAL RAMUS (ApRm): a distally directed rod arising from the base of the distal
arms in Albia.
APICAL SETA (ApSt): a simple seta borne on the distal arm sclerite or on an apical
development of the sclerite.
ARM RAMUS: a Short, posteriorly directed rod arising from the base of the proximal
arm; known only from Unionicola.
AXILLARY: positioned in or near the angle between the distal arm and the lateral
surface of the midsection of the EC.
BASAL PLATE (BsPl): a sclerotized plate of varying dimensions, subtending the
proximal arm and lying in the lateral walls of the proximal chamber and/or
the midsection of the EC.
CARRIER FLUID: a secretory product of the testes noted by Schmidt (1935) and
evident in sections of the testes and seminal vesicles of Hydrodroma; having a
characteristic, globular histological appearance and presumably functioning as
a transportation medium for the spermatozoa.
CHAMBER (Cmb): any widening of the sperm passage (q.v.); walls may be mem-
branous or sclerotized.
CHAMBER RAMUS (CmbRm): a short, usually anteriorly directed rod or plate, arising
from the base of the proximal arm and lying in the lateral wall of the
proximal chamber.
75
DISTAL: pertaining to the free, unattached tip of any structure, the end farthest
from. any connection with a larger body; (DISTAD: in the distal direction).
DISTAL ARM (DisAm): a sclerotized rod (in the generalized condition) projecting
laterally from the distal area of the EC, subtended by the distal arm sclerite:
variously reduced and modified in different genera.
DISTAL ARM SCLERITE: One Of a pair of sclerites situated on either side of the distal
end of the EC; composed of three main rami and often produced distad into
an apical development.
DISTAL MEMBRANES: a cone of lightly sclerotized membranes inserting around the
EC, usually in its distal half, and attaching it to the borders of the genital
opening in the body wall; these membranes thus form the walls of the phallo-
crypt (q.v.).
DISTAL RAMUS (DisRm): a distally directed rod arising from the proximal arm
sclerite; usually lying lateroposteriorly in walls of midsection of EC.
DISTAL ROD (DisRd): a distally directed, sclerotized rod arising from the distal
border of the proximal keel; lying along the median line.
DISTAL SCLERITE (DisSc): any sclerite lying distally in the midsection of the EC;
usually laterally, but three posterior pairs are noted for Hydrodroma.
DISTOLATERAL BORDER (DIBd): referring to this edge of the proximal chamber, often
Strengthened by a sclerotized extension of the anterior margin sclerite.
DUCTUS EJACULATORIUS: the tube-like terminal portion of the male reproductive
system; formed by fusion of the paired vasa deferentia.
EJACULATORY COMPLEX (EC): the well-muscled, chitinous framework of the walls
of the distal portion of the ductus ejaculatorius (q.v.); functioning to form,
exsert, and deposit spermatophores (q.v.).
ENDOSTERNITE: a transverse bundle of endocuticular fibers lying just anterior to
the EC in the body of Hydrodroma; serving as a point of origin for various
body muscles.
GENITAL ACETABULUM: usually subcircular cuticular structures in the region of the
external genitalia of almost all adult water mites; function probably sensory.
GENITAL OPENING: external opening in the body wall through which the genital pro-
ducts pass.
GENITAL PLATE: a Sclerotized plate lying in the ventral body wall in close proximity
to the genital opening.
KEEL: any flat, sclerotized, longitudinally oriented plate projecting from the median
line of the EC.
LATERAL: a directional term having the same meaning for the EC as for the adult
mite; (LATERAD: in a lateral direction).
LATERAL SHELF (LtrSf): a thin, sclerotized, subtriangular plate of varying size, join-
ing the distal arm to the lateral wall of the midsection of the EC.
LATERAL WALL SCLERITE (LWScl): a rod-like, (usually) oblique sclerite situated in
the lateral wall of the proximal chamber.
MIDSECTION: that area of the EC lying distal to the proximal chamber and proximal
to the distal arm sclerites.
PHALLIC RETRACTOR: a small group of three muscle fibers having its origin on the
lateral end of the endosternite and inserting near the base of the distal arm,
apparently serving to withdraw the EC after spermatophore deposition.
76
PHALLOCRYPT: an invagination of the ventral body wall to form a protected (yet
topologically external) cavity into which projects the distal tin of the EC.
POSTERIOR: that surface of the EC usually facing in a posteroventral position when
the organ is in situ; the surface opposite that through which the ductus ejacu-
latorius enters the EC.
POSTERIOR KEEL (PosKl): a thin, plate-like structure, usually borne medially on the
posterior surface of the proximal chamber, often roughened for muscle attach-
ment.
POSTERIOR RAMUS (PostRm): a proximally directed, rod-like sclerite arising from
the base of the distal arm sclerite, usually lying in the posterior and/or lateral
walls of the midsection.
POSTEROLATERAL SCLERITE: a thickened, rod-like sclerotization lying laterally in the
posterior surface of the distal third of the Hydrodroma EC.
PROXIMAL: pertaining to the basal, attached end of any structure, the end closest
to any connection with a larger body; (PROXIMAD: in the proximal direction).
PROXIMAL ARM (PrxAm): an elongate, rod-like sclerite, projecting laterad from the
body of the EC at approximately the level of the distal border of the proximal
chamber; subtended by the proximal arm sclerite (q.v.).
PROXIMAL ARM SCLERITE: one Of a pair of sclerites situated, one on either side of
the body of the EC, proximally; composed of four main rami.
PROXIMAL CHAMBER (PrxCmb): a large median chamber in the proximal-most por-
tion of the EC, constant in occurrence; constituting that part of the EC which
receives semenaceous material directly from the ductus ejaculatorius.
PROXIMAL HORN (PrxHn): one of a pair of short, rod-like, sclerotized projections
sometimes occurring on the anteroproximal border of the proximal chamber.
PROXIMAL RAMUS: a median, sclerotized, proximally directed projection of the
anteroproximal border of the proximal chamber; often bearing the proximal
horns (q.v.).
PROXIMAL SCLERITE (PrxSc): any sclerite lying proximally, in the anterior or
lateral walls of the midsection.
SEMINAL VESICLE: One of a pair of anteroposteriorly elongate, thin-walled sacs col-
lecting spermatozoa from the sperm ducts and acting as a reservoir; sperma-
tozoa leave anteriorly via the vasa deferentia.
SPERMATOPHORE: a discrete unit of transfer containing a quantity of viable sperma-
tozoa; of simple or complex structure; often complicated by the presence of a
stalk or other hold-fast device; of wide occurrence in the Acari.
SPERM PASSAGE: the central cavity of the EC through which spermatozoa must
pass.
TESTIS: the male water mite reproductive gland, producing spermatozoa and carrier
fluid.
VAS DEFERENS: one Of a pair of short, thin-walled tubes carrying semen anteriorly
away from the seminal vesicles; the tubes fuse distally to form the median
ejaculatory duct.
af
Acknowledgments
This report was adapted from a thesis submitted to the Faculty of the
Graduate School of Cornell University, June 1969, in partial fulfilment of
the requirements for the degree of Doctor of Philosophy.
I thank Dr. W. L. Brown, Jr. for his constructive criticism and
advice during the course of the work and for a stimulating introduction
to the principles of evolutionary theory. Dr. G. B. Wiggins gave early
encouragement to my systematic interest in invertebrates and provided a
basic instruction in systematic method. I am further indebted to Drs.
Rodger Mitchell, David R. Cook, and Carmine A. Lanciani for advice
and discussions on many aspects of water mite classification, evolution,
and biology. Numerous colleagues have supplied useful reprints of their
articles.
Support for the study came from two Fellowships and a Comstock
Scholarship awarded by Cornell University, and from a two-year Special
Scholarship granted by the National Research Council (Canada). A fund
provided by the Allied Chemical Company supplied financial assistance
for research and travel during the period 1965 - 1968.
Dr. Robert C. Dalgleish kindly made it possible to collect on the
Edmund Niles Huyck Preserve, and the New York Finger Lakes State
Parks Commission supplied the author with a permit to collect in several
state parks. Part of the material was collected in Ontario by Mr. I. M.
Smith for the Department of Entomology and Invertebrate Zoology, Royal
Ontario Museum.
Acknowledgment is made for use of the scanning electron microscope
in the Royal Ontario Museum, established through a grant from the
National Research Council to the Department of Zoology, University of
Toronto, for the development of a programme in systematic and evolu-
tionary zoology.
My wife, Carrolyn, was of great assistance, both through her patience
during the research and as an indefatiguable collector of water mites.
Miss Alix E. Hillmer typed several drafts of the manuscript and assisted
with the task of proof-reading and editing. Mr. Anker Odum, Scientific
Illustrator in the Department of Entomology and Invertebrate Zoology,
Royal Ontario Museum, gave valuable advice in the preparation of figures
and plates.
78
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*References not seen by the author.
83
Appendix A: Traditional Classification of Water Mites
(adapted from Viets and Viets, 1960)
HYDRACHNELLAE
Hydrovolziae:
Hydrachnae:
Limnocharae:
Hydryphantae:
Lebertiae:
Pionae:
Axonopsae:
Mideopsae:
Krendowskiae:
Arrenurae:
*These New World genera were not included by Viets and Viets (1960) and so
Hydrovolziidae:
Hydrachnidae:
Limnocharidae:
Eylaidae:
Protziidae:
Thyasidae:
Hydryphantidae:
Hydrodromidae:
Pseudohydryphantidae:
Sperchonidae:
Lebertiidae:
Oxidae:
Torrenticolidae:
Limnesiidae:
Hygrobatidae:
Unionicolidae:
Feltriidae:
Pionidae:
Axonopsidae:
Aturidae:
Mideidae:
Mideopsidae:
Krendowskiidae:
Arrenuridae:
Hydrovolzia
Hydrachna
Limnochares
Eylais
Protzia
Thyas
Hydryphantes
Hydrodroma
Pseudohydryphantes
Sperchon, Sperchonopsis
Lebertia
Frontipoda, Oxus
Testudacarus*, Torrenticola
Limnesia, Tyrrellia*
Atractides, Hygrobates
Koenikea*, Neumania, Unionicola
Feltria
Forelia, Piona, Tiphys
Albia, Brachypoda, Axonopsis
Aturus, Kongsbergia
Midea
Mideopsis
Geayia*
Arrenurus
have been inserted above on the basis of Mitchell’s (1954) checklist.
Appendix B: Johnston’s Classification (1965) of Water Mites (adapted)
ACARIFORMES — PARASITENGONA
Calyptostomoidea:
Erythraeoidea:
Trombidioidea:
Hydrovolzioidea:
Eylaoidea:
Hydryphantoidea:
Calyptostomidae
Erythraeidae, Smarididae
Trombiculidae, Trombidiidae (s. lat.)
Hydrovolzia
Eylais, Limnochares
Hydrodroma, Hydryphantes, Protzia, Thyas
HYDRACHNELLAE (s. str.)
Hydrachnoidea:
Lebertoidea:
Hygrobatoidea:
Aturoidea:
Mideopsoidea:
Acalyptonotoidea:
Arrenuroidea:
*The position of these genera was not given by Johnston (1965).
Hydrachna
Frontipoda, Lebertia, Oxus, Pseudohydryphantes*,
Sperchon, Sperchonopsis, Testudacarus, Torrenticola
Atractides, Feltria, Forelia, Hygrobates, Koenikea,
Limnesia, Neumania, Piona, Tiphys, Tyrrellia,
Unionicola
Albia*, Aturus, Axonopsis, Brachypoda, Kongsbergia
Midea, Mideopsis
Geayia
Arrenurus
inserted above on the basis of Mitchell’s (1954) checklist.
84
They have been
Appendix C: Data For Specimens Examined
Collections are deposited in the Department of Entomology and Inverte-
brate Zoology, Royal Ontario Museum.
Albia sp. (nr. A. caerulea) (p. 24)
ONT.: Baysville, Muskoka Dist.; Echo L., Sta. xv; 22 auG 1965, I. M. Smith.
Arrenurus crenellatus (p. 26)
N.Y.: Rensselaerville, Albany Co.; Lake Myosotis, E. N. Huyck Preserve;
3 SEPT 1966, D.B.
A. intermedius (p. 27)
As above.
A. lyriger (p. 27)
AS above.
A. magnicaudatus (p. 27)
N.Y.: Dryden, Tompkins Co., Dryden Twp.; Dryden Lake; 21 JUNE 1966,
D.B.
A. major (p. 27)
N.Y.: Rensselaerville, Albany Co.; Lincoln Pond, E. N. Huyck Preserve;
3 SEPT 1966, D.B.
Ae planus (p. 27)
ONT.: Aberfoyle, Wellington Co.; pond 1; 16 MAY 1967, I. M. Smith.
A. semicircularis (p. 29)
N.Y.: Rensselaerville, Albany Co.; Lake Myosotis, E. N. Huyck Preserve;
3 SEPT 1966, D.B.
A. trifoliatus (p. 29)
As above.
A. wardi (p. 29)
N.Y.: Rensselaerville, Albany Co.; Lincoln Pond, E. N. Huyck Preserve;
3 SEPT 1966, D.B.
Atractides sp. (p. 29)
ONT.: Kendal, Durham Co.; cold, fast stream; 31 MAY 1966, I. M. Smith.
Aturus, (Ss. str.) sp. (nr. A. deceptor) (p. 31)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.; Cayuga Inlet at Rt. 34; 26 AuG 1966,
D.B.
Axonopsis (Hexaxonopsis) sp. (p. 32)
N.Y.: Slaterville Springs, Tompkins Co., Caroline Twp.; Six Mile Creek, CU
wildflower preserve; 15 JULY 1966, D.B.
Brachypoda (s. str.) sp. (nr. B. cornipes) (p. 32)
N.Y.: Myers, Tompkins Co., Lansing Twp.; Cayuga Lake at Lansing Park;
> JUNE 1967, DB.
Eylais sp. (p. 33)
ONT.: Aberfoyle, Wellington Co.; temp. pond 1; 15 MAy 1966, I. M. Smith.
Feltria sp. (p. 35)
ONT.: Kendal, Durham Co.; moss, cold fast stream; 16 JUNE 1967, I. M. Smith.
Forelia (Madawaska) borealis (p. 35)
N.Y.: Rensselaerville, Albany Co.; Lincoln Pond, E. N. Huyck Preserve;
SeSEPT 1966, D:B.
Frontipoda sp. (p. 36)
N.Y.: Rensselaerville, Albany Co.; Lake Myosotis, E. N. Huyck Preserve;
3 SEPT 1966, D.B.
Geayia sp. (p.37)
ont.; Chatifey's WLocks; Ieeds..Go.; Lake Opinicon, Sta. v; 27 MAY 1965,
I. M. Smith.
Hydrachna (Rhabdohydrachna) sp. (p. 39)
ONT.: Kendal, Durham Co.; pond 1; 3 JUNE 1967, I. M. Smith.
85
Hydrovolzia sp. (p. 39)
ALTA.: Banff; spring fed stream, road to Sundance Canyon; 22 JUNE 1962, D.B.
Hydryphantes sp. (nr. H. ruber) (p. 40)
N.Y.: Waterburg, Tompkins Co., Ulysses Twp.; temp. pond s. of Indian Fort
Road; 5 MAY 1966, D.B.
Hygrobates sp. (p. 40)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.: Cayuga Inlet at Rt. 34; 26 auG 1966,
D.B.
Koenikea sp. (p. 41)
N.Y.: Rensselaerville, Albany Co.; Lake Myosotis, E. N. Huyck Preserve;
3 SEPT 1966, D'B:
Kongsbergia sp. (p. 43)
ONT.: Caledon, Peel Co.; stream on Caledon sideroad no. 5; 12 SEPT 1966,
I. M. Smith.
Lebertia sp. (p. 44)
N.Y.: Myers, Tompkins Co., Lansing Twp.; Cayuga Lake at Lansing Park;
20 AuG 1966, D.B.
Limnesia (Ss. Sir.) Sp.) (Gps 4)))
N.Y.: Dryden, Tompkins Co., Dryden Twp.; Dryden Lake; 16 APR 1966, D.B.
Limnochares sp. (nr. L. americana) (p. 47)
N.Y.: Dryden, Tompkins Co., Dryden Twp.; Dryden Lake; 24 auc 1966, D.B.
Midea sp. (p. 47)
ONT.: Chaffey’s Locks, Leeds Co.; Lake Opinicon, Sta. vm; 5 sepT 1965,
I. M. Smith.
Mideopsis sp. (p. 48)
As above.
Neumania sp. (p. 49)
N.Y.: Dryden, Tompkins Co., Dryden Twp.; Dryden Lake; 24 auc 1966, D.B.
Neumania sp. (nr. N. distincta) (p. 51)
N.Y.: Rensselaerville, Albany Co.; Lake Myosotis, E. N. Huyck Preserve;
3°SEPT 1966; DB.
Oxus sp. (nr. O. connatus) (p. 51)
As above.
Oxus sp. (nr. O. intermedius) (p. 52)
As above.
Piona pinguipalpis (p. 52)
N.Y:: Waterburg, Tompkins Co., Ulysses Twp.; temp. pond s. of Indian Fort
Road; 5 MAY 1966, D.B.
Protzia: sp. (p. 53)
ONT.: Kendal, Durham Co.; cold, fast stream; 31 MAY 1966, I. M. Smith.
Pseudohydryphantes sp. (p. 55)
ONT.: Baysville, Muskoka Dist.; Echo L., Sta. xv; 20 JULY 1966, I. M. Smith.
Sperchon sp. (p. 56)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.; Cayuga Inlet at Rt. 34: 25 JUNE
1966, D.B.
Sperchonopsis sp. (p. 57)
ONT.: Kendal, Durham Co.; cold, fast stream; 31 MAY 1966, I. M. Smith.
Testudacarus sp. (p. 57)
ONT.: Kendal, Durham Co.; cold, fast stream; 16 JUNE 1967, I. M. Smith.
Thyas barbigera (p. 59)
N.Y.: Waterburg, Tompkins Co., Ulysses Twp.; temp. pond s. of Indian Fort
Road; 5 MAY 1966, D.B.
Tiphys sp. (nr. T. americana) (p. 60)
ONT.: Port Credit, Peel Co.; pond v; 21 May 1966, I. M. Smith.
Torrenticola sp. (designated species A) (p. 60)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.; Cayuga Inlet at Rt. 34; 26 AUG
1966, D.B.
86
Torrenticola sp. (designated species B) (p. 61)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.; Cayuga Inlet at Rt. 34; 5 auG
1966, D.B.
Pyrrellia sp. (p. 61)
N.Y.: Ithaca, Tompkins Co., Ithaca Twp.; Buttermilk Ck. at 500 ft. elev.;:
26 JULY 1966, D.B.
Unionicola sp. (p. 63)
N.Y.: Dryden, Tompkins Co., Dryden Twp.; Dryden Lake; 30 JULY 1966, D.B.
87
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