A Review of the North American Freshwater Snail Genus Pyrgulopsis

NUMBER 554
ANSP 61606; paralectotypes, ANSP 375747. Pyrgulopsis
wabashensis: Wabash River, at The Chains in Posey County,
Indiana. Lectotype (Baker, 1964:177), ANSP 27824; paralectotypes,
ANSP 96607, ANSP 396953.
DISTRIBUTION.—Ohio, Mississippi, Tennessee River drainages,
eastern United States (very incompletely known).
REMARKS.—Wolf (1869) described Pyrgula scalariformis
from empty shell collected along the Illinois River. Pilsbry
(1886) introduced Pyrgula scalariformis mississippiensis in a
short note based on empty shell collected along the Mississippi
River (Illinois side). Later in the same year, Call and Pilsbry
fully described Pyrgulopsis mississippiensis,' with the above
listed as a synonym followed by the comment (1886:13), "No
description." Clench and Tlirner (1962:99) and others have
treated the earlier name as a nomen nudum, however, Pilsbry
(1886) did provide a description of this taxon ("...smaller,
stouter than typical fossil scalariformis, and more compactly
coiled-never exhibiting the peripheral carina on upper whorls.
The shorter forms remind one of the common rhomboidal
variety of Anculosa dissimilis Say."), thus rendering the name
valid under ICZN Article 12. Fortunately the authorship of
mississippiensis is not a critical issue given its status as junior
subjective synonym of scalariformis Wolf, 1869 (see below).
Shimek (1892) argued that the differences between scalariformis
and mississippiensis reported by Call and Pilsbry (1886;
stronger carina of shells of the former, and different aperture
and sutures) are not consistent when a large series of specimens
is examined. The author concurs, and suggests that a single
species, with variable carina development, is involved. Hinkley's
(1908) description of wabashensis emphasized the
absence of a carinate body whorl; in fact many of the paratypes
and other material from the type locality are carinate and very
closely resemble some scalariformis. Although Wabash River
shells are usually small and occasionally quite narrow, I see no
reason to consider them a separate species from the above. A
completely satisfactory treatment of this problem is precluded
by paucity of anatomical material for these animals. Two of the
three taxa (scalariformis, mississippiensis) were described
from empty shell and all three apparently are extinct at their
respective type localities. Living material later was obtained
from the rather distant locality (Tennessee River drainage) of
Shoal Creek, Alabama (Hinkley, 1906; Walker, 1906; operculum
and radula figured by Baker [1928]); as well as Meramec
River, Missouri (FSM collections). Unfortunately no alcoholpreserved
material is available for the Shoal Creek population,
which may no longer be extant (Fred G. Thompson, pers.
comm., 5/1992), and only a few such specimens are available
TABLE 2.—list of character-state transformations at ancestral nodes
(defining clades of interest) on the consensus tree (Figure 53).
Clade 1: 2-1, 4-1, 7-1. 8-1,13-1,14-1,15-1, 16-1.18-1,19-1, 24-1.47-1,54-1, 55-1,61-1
Clade 2: 2-2, 8-0, 17-1, 20-2. 31-0.48-1,49-1, 57-1, 58-2, 62-0
Clade 3: 29-3,31-3,49-0
Clade 4: 9-1, 35-1,36-1,37-2,40-1
Clade 5: 9-1, 32-1, 33-1, 34-1,47-0
from the Meramec River, thus providing a meager sample for
the snail.
MATERIAL EXAMINED.—FSM 91725, Meramec River, 2.9
km north-northwest of Steeleville, Crawford County, Missouri;
FSM 91726, ibid., 12.0 km southeast of Leesburg.
Cladistic Analysis
The "m* M option produced a single tree of consistency index
of 0.26 and retention index of 0.61. Branch and bound ("bb*")
search based on this tree yielded more than 1559 trees of equal
length. The "nelsen" option then was used to obtain a strict
consensus tree for these solutions, which is shown in Figure 53.
Lists of character-state transformations supporting clades of
interest are in Table 2.
The consensus tree provides support for monophyly of
Pyrgulopsis (referred to as Clade 1 in Table 2) in that our genus
is differentiated from the outgroup by 15 character-state
transformations, including six non-homoplasious synapomorphies:
densely pitted protoconch (character 3-1), broad operculum
attachment scar (8-1), narrow basal process on central
radular tooth (16-1), well developed lateral angles of central
tooth (17-1), simple anterior vas deferens (25-1), and horizontally
oriented bursa copulatrix (55-1).
Within Pyrgulopsis, four large clades are reasonably
supported and may merit recognition as species groups. The
nine eastern American species (Clade 2), comprising all species
allocated to Marstonia by Thompson (1977) plus P. scalariformis,
are defined by 10 character-state transformations,
including non-homoplasious synapomorphies of coarse protoconch
microsculpture (3-2) and anterior junction between
oviduct and bursal duct (49-1). Homoplasious characters
supporting this clade include a banded pattern of mantle
pigmentation (18-1; reversed in one eastern species), narrowly
vertical oviduct coil (50-1; reversed or transformed in two
eastern species), elongate bursal duct (58-1; paralleled in a
western species), and bursal duct deeply embedded in albumen
gland (59-2; reversed in one eastern species). Other characters
uniquely, but not universally, found in this clade are an
incomplete inner shell lip (2-1), indented outer edge of
operculum (7-1), strongly oblique penial lobe (29-1), and
narrow, sac-like bursa copulatrix (53-3). Members of this clade
have ovate-conic shells and relatively simple penes usually
ornamented by a terminal gland and, in some cases, a ventral
gland.
The other three clades are comprised of subsets of the
western American fauna. Six species from southern Nevada
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