A Review of the North American Freshwater Snail Genus Pyrgulopsis

NUMBER 554 11
studied the anatomy of our genus. Hershler and Thompson
(1987) supported this allocation after determining that members
of the genus have the glandular, distally bifurcate penis,
and female capsule gland with enclosed ventral channel
characteristic of the subfamily.
The Nymphopilinae are comprised of eight North American
genera: Birgella, Cincinnatia, Notogillia, Nymphophilus, Pyrgulopsis,
Rhapinema, Spilochlamys, and Stiobia. Thompson
(1979) also referred six European genera (subfamily
Orientalininae (= Orientaliinae)) to the Nymphophilinae, but
additional study of these and comparison with North American
forms is necessary to corroborate these allocations 1 . Phylogenetic
relationships among the nymphophiline genera are not
known and although the anatomy of each has been studied to a
certain extent (notably by Thompson, 1968, 1969, 1979, 1984;
Thompson and McCaleb, 1978), important details such as
morphology of the distal female genitalia are lacking for some
of them. (The author currently is reviewing these taxa in order
to obtain a complete morphological data set and prepare a
phylogenetic analysis.)
Birgella, Rhapinema, and Nymphophilus share with
Pyrgulopsis a relatively simple penis with few glands and
accessory lobes, but differ in their larger, thicker, broader
shells. Based on my limited study of these genera, Nymphophilus,
locally endemic in northern Mexico, appears to be closest
to Pyrgulopsis as these taxa share several other possibly
derived features such as shell with wrinkled or punctate
protoconch and basal keel (the latter present in only some
species of Pyrgulopsis) 2 .
Apart from shell, Pyrgulopsis differs from Nymphophilus in
its more densely punctate protoconch, paucispiral (versus
multispiral) operculum, relatively larger attachment region on
ventral operculum, narrower central radular tooth, narrower
1 Based on published illustrations, only two of these genera (see below) have
penial glands, while the others resemble nymphophilines only to the extent that
their penes are distally bifurcate. The Orientalininae, which Thompson (1979)
placed in synonymy with the Nymphophilinae, is a very large group comprising
many more than the six genera listed by Thompson (see Radoman, 1983): it is
not clear whether any of these other taxa can plausibly be referred to the
Nymphophilinae.
2 Although most species of Pyrgulopsis have the simple penis described above,
variation within the group is high, further complicating recognition of its
sister-group. However, the more elaborately ornamented penis of species such
as P. californiensis and P. wongi only partly achieves the complexity of glands
and accessory lobes typical of other nymphophiline genera such as Cincinnatia,
and thus I suspect that such a sister group relationship (previously postulated by
Hershler and Thompson, 1987) is less likely than that advocated above.
Regrettably, the intriguing possibility that Pyrgulopsis instead is more closely
related to either of two European genera (Avenionia, Liithabitella) also
endowed with penial glands (see Boeters, 1970, fig. 1; 1974, figs. 6, 7; Boeters
and Winter, 1983, figs. 1-9) cannot be meaningfully explored at this time.
basal process of central tooth, more developed lateral angles of
central tooth, narrower central cusps on central and lateral
radular teeth, simpler gonadal morphology, generally horizontal
(as opposed to transverse) bursa copulatrix, and simple
anterior vas deferens (not comprising a raised ridge on
neck)(data for Nymphophilus from Taylor, 1966b; Thompson,
1979; Hershler, 1985; pers. obs.).
I continue to embrace the broad concept of Pyrgulopsis
proposed by Hershler and Thompson (1987). The earlier
separation of Pyrgulopsis from other nymphophilines now
considered junior synonyms may be attributable to the scant
attention paid to hydrobiid snail anatomy by North American
workers until recently 3 , and undue significance attached to the
presence of a basal keel on the shell of Pyrgulopsis (sensu lato).
It is of interest to note, with regard to the latter, that western and
eastern carinate forms do not comprise a clade within the genus
and may represent convergent shell forms (see "Cladistic
Analysis")- Anatomical comparisons also were historically
hampered by the fact that the type species of our genus, P.
nevadensis, probably has been extinct for much of this century.
The discovery (from resuscitated dried material; Hershler and
Thompson, 1987) that the penis of this species is similar in
form and glandular endowment to other North American
genera paved the way for the revised concept of Pyrgulopsis
used herein.
The following remarks on taxa placed in synonymy with
Pyrgulopsis are intended as supplemental to the brief comments
provided by Hershler and Thompson (1987).
Baker (1926) erected Marstonia as a subgenus of Amnicola,
distinguished from Amnicola s.s. by its small nuclear whorl and
longer, sharper radular cusps, and placed six eastern species in
this group. Baker (1928) later added additional, principally
northern lacustrine taxa to the group. Taylor (1960b) first
treated Marstonia as a separate genus, although justification for
such was not provided. Thompson (1977) reviewed the genus
(recognizing eight species), demonstrated that it belonged in
the Nymphophilinae, and suggested that some eastern species
described as Pyrgulopsis may belong to Marstonia. While there
are no features consistently separating species assigned to
Marstonia by Thompson from other members of our genus, it
is clear that eastern Pyrgulopsis, including the above plus
carinate forms, comprise a species group distinct from western
forms (see "Cladistic Analysis").
Gregg and Taylor (1965) described Fontelicella, comprised
of three subgenera and twelve western American species. They
3 An exception being the fine early anatomical work of Berry (1943), which
included illustrations of the penis of eastern Pyrgulopsis letsoni showing a
distal lobe endowed with a single gland. Unfortunately this observation went
unnoticed by later workers who described new genera for animals with similar
penes.