A Review of the North American Freshwater Snail Genus Pyrgulopsis

A Review of the North American Freshwater
Snail Genus Pyrgulopsis (Hydrobiidae)
Introduction
Prosobranch snails of the genus Pyrgulopsis are widespread
in the United States (extending into southern Canada) and
northern Mexico, where they occur in lakes, springs, seeps,
marshes, and diverse lotic waters. These small (about 1-8 mm
shell length) animals often are found in densities exceeding
>1000/m 2 (for example see Noel, 1954), comprising a
prominent element of the benthic epifauna. Pyrgulopsis, as
recognized herein, is the second most diverse genus of North
American freshwater gastropods (the pleurocerid Elimia ranking
as first) and includes many narrowly localized species.
Numerous undescribed species also are known, and large
physiographic regions still await exploration by those interested
in these easily overlooked organisms. These snails are
beginning to draw the attention of wildlife agencies and groups
seeking to preserve and manage North American aquatic
ecosystems: over half (52%) of the Pyrgulopsis species
recognized herein currently are candidates for addition to the
Federal List of Threatened and Endangered Species (USDI,
1991a) and three snails (from New Mexico and Idaho) recently
were listed as endangered (USDI, 1991b, 1992,1993). At least
three members of the genus have gone extinct since their
original description during the early part of this century.
Call and Pilsbry (1886) erected Pyrgulopsis for four species
from the United States having a small, fairly elongate shell
whose single basal carina distinguished the group from
multicarinate European Pyrgula. Ancey (1888) early reviewed
Pyrgulopsis, and described 13 new Central American taxa, all
of which were later transferred to the hydrobiid subfamily
Cochliopinae, genus Pyrgophorus, by Hershler and Thompson
(1992). Wenz (1926) also provided an early review of fossil
species assigned to this genus. The concept of this group varied
little since that time (even recent workers such as Burch (1982)
and Taylor (1985) used Pyrgulopsis in the original sense) until
Robert Hershler, Department of Invertebrate Zoology, National
Museum of Natural History, Smithsonian Institution, Washington,
D.C. 20560.
Robert Hershler
Hershler and Thompson (1987) redefined the genus in a
broader fashion based on penial (rather than shell) characters.
They consequently placed five other North American genuslevel
taxa in synonomy with our group, which as a result
swelled to 24 Recent species. The relationship between
Pyrgulopsis (sensu Hershler and Thompson) and two similar
genera recently described from the West (Taylor, 1987) has not
been addressed in the literature.
The scope and content of Pyrgulopsis remain incompletely
known because the anatomy of relatively few North American
freshwater hydrobiids has been studied—this includes some of
the species allocated to the genus, on a provisional basis, by
Hershler and Thompson (1987) and other, mostly western
hydrobiids with simple, ovate-conic shells that were early
described as members of "catch-all" genera such as Amnicola
and Paludestrina.
There has been no comprehensive review of the species of
Pyrgulopsis since that of Ancey (1888), at which time only two
of the 65 species considered valid herein had been described.
The present review is intended to provide nomenclatural
stability for Pyrgulopsis and its Recent species, and is based on
evaluation of available type and other museum material as well
as anatomical study of almost all Recent North American
hydrobiid snails potentially referable to the genus.
Pyrgulopsis species usually are readily distinguished from
one another by combinations of qualitative characters, and thus
I have not gathered and analyzed quantitative morphological
data as part of this broad review. Note, however, that analysis
of such data has been previously pursued with good results in
studies of local Pyrgulopsis faunas (Hershler and Sada, 1987;
Taylor, 1987; Hershler and Landye, 1988), and use of this and
other means of comparing populations (i.e., biochemical) will
be necessary to better resolve the lingering species-level
problems in this group.
Only nominate taxa are included in this review, as my
intention is to provide herein a framework for future studies
describing new species. Eastern American Pyrgulopsis were
included despite the fact that most of them recently were well