MALACOLOGIA, 1984, 25(1): 109-141
NORTH AMERICAN FRESHWATER SNAIL GENERA
OF THE HYDROBIID SUBFAMILY LITHOGLYPHINAE
Fred G. Thompson
Florida State Museum, University of Florida, Gainesville, Florida 32611, U.S.A.
ABSTRACT
The classification of the North Аглепсап genera of Lithoglyphinae is reviewed, based on
anatomical and conchological characters. Five genera are recognized: Gillia Stimpson, 1865,
Fluminicola Stimpson, 1865, Somatogyrus Gill, 1863, Clappia Walker, 1909, and Lepyrium Dall,
1896. The North American genera are conservative in their anatomies. Primary morphological
differentiations involve radular and shell characters. The North American genera are demon-
strated to have evolved through trophic specializations and microhabitat specializations.
Lepyrium Dall, 1896, formerly considered a monotypic family, is closely related to Clappia and
Somatogyrus. Birgella Baker, 1926, is removed from the Lithoglyphinae, where it has been
placed by authors, and is demonstrated to be in the Nymphophilinae. The following species are
described in detail: Lepyrium showaiteri (Lea, 1861), Somatogyrus rheophilus n. sp., Gillia altilis
(Lea, 1841). A neotype is designated for the latter species.
Key words: Gastropoda, snails, Hydrobiidae, Lepyriidae, Lithoglyphinae, Lepyrium, Clappia,
Somatogyrus, Gillia, Fluminicola, systematics, evolution.
INTRODUCTION
This paper discusses the systematic rela-
tionships between the North American litho-
glyphine genera: Lepyrium, Somatogyrus,
Clappia, Gillia, and Fluminicola (Class GAS-
TROPODA, Subclass PROSOBRANCHIA, Order
MESOGASTROPODA, Family HYDROBIIDAE,
Subfamily LITHOGLYPHINAE). A sixth genus,
Antrobia Hubricht, 1972, is placed by Burch &
Tottenham (1980: 100) in the Lithoglyphinae.
It is a monotypic genus from a cave in Mis-
souri; the anatomy remains undeschbed and
Antrobia is omitted from further discussion in
this paper. Another genus, Cochliopina Morri-
son, 1946, traditionally has been associated
with the Lithoglyphinae. Hershler (in press)
shows that it is a genus of the Littohdininae.
Birgella Baker, 1926, Is another genus that
has been confused with this subfamily, even
as recently as 1981 (Clarke). It is in the NYM-
PHOPHILINAE, as is discussed in Appendix B.
This study stems from two independent
investigations. The first was an attempt to
determine species-group characteristics with-
in Somatogyrus, a genus containing many
species (Burch & Tottenham, 1980: 104-
106). The study was tabled temporarily be-
cause very little anatomical diversity was dis-
covered among the species examined. In-
dependently I examined the anatomy of
Lepyrium showaiteri (Lea), a snail previously
placed in a monotypic family of uncertain
affinity within the MESOGASTROPODA (Pilsbry
& Olsson, 1951). Its soft anatomy was found
to be hardly distinguishable from that of
Somatogyrus. These two genera have very
dissimilar shells, but they have in common
similar habitats. Lepyrium and most Somato-
gyrus live on rocks and boulders in high-
energy rivers. The habitat deployments
among these two genera focus on the adap-
tive radiation of the Lithoglyphinae in eastern
North America. In order to clarify the limits of
this basic radiation other relevant genera
were examined. The results of these studies
are presented herein.
MATERIAL AND METHODS
Anatomical descriptions and illustrations in
this paper are based upon the following speci-
mens:
Lepyrium showaiteri (Lea). Two lots of
about 100 specimens each, collected June
21 , 1 978 (UF 31 343) and June 22, 1 978 (UF
31342) in the Little Cahaba River, 2.4 km
upstream from the Cahaba River, Bibb Co.,
Alabama by F.G.T. Relaxed with menthol
crystals, fixed in Bouin's solution and pre-
served in 70% ethanol.
Somatogyrus rheophilus n. sp. (described
below). One series of thousands of speci-
(109)
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