Marstonia
Introduction '''''Marstonia''''' is a genus of freshwater snails with a gill and an operculum, aquatic gastropod molluscs in the family Hydrobiidae.
Distribution Species in the genus ''Marstonia'' are distributed in springs, streams and lakes in eastern North America. Most of these species have extremely narrow geographic ranges and consequently have become a focus of conservation activities; two are federally listed as endangered and others are variously listed by state wildlife agencies.
Description The freshwater gastropod genus ''Marstonia'' is composed of 15 small (shell height < 5.0 mm), ovate- to elongate-shelled species. ''Marstonia'' differs from the other eight North American nymphophiline genera in that the (female) oviduct and bursal duct join well in front of (instead of behind) the posterior wall of the pallial cavity. It has also been resolved as a well supported sub-clade within its subfamily based on mtDNA sequences.
Species Eastern North American species of ''Pyrgulopsis'' are considered to be in separate genus ''Marstonia'' according to Thompson & Hershler (2002). * ''Marstonia agarhecta'' (F. G. Thompson, 1969) - synonym: ''Pyrgulopsis agarhecta'' F. G. Thompson, 1969 - Ocmulgee marstonia* ''Marstonia arga''  - F. G. Thompson, 1977 - synonym: ''Pyrgulopsis arga'' (F. G. Thompson, 1977) - ghost marstonia* ''Marstonia castor'' F. G. Thompson, 1977 - synonym: ''Pyrgulopsis castor'' (F. G. Thompson, 1977) - beaverpond marstonia* ''Marstonia halcyon'' F. G. Thompson, 1977 - synonym: ''Pyrgulopsis halcyon'' (F. G. Thompson, 1977) - halcyon marstonia* ''Marstonia hershleri'' (F. G. Thompson, 1995) - synonym: ''Pyrgulopsis hershleri'' F. G. Thompson, 1995 - Coosa pyrg* ''Marstonia letsoni'' (Walker, 1901) - synonym: ''Pyrgulopsis letsoni'' (Walker, 1901) - gravel pyrg* ''Marstonia lustrica'' (Pilsbry, 1890) - synonym: ''Pyrgulopsis lustrica'' (Pilsbry, 1890) - boreal marstonia* ''Marstonia ogmorhaphe'' (F. G. Thompson, 1977) - synonym: ''Pyrgulopsis ogmoraphe'' (F. G. Thompson, 1977) - royal springsnail* ''Marstonia olivacea'' (Pilsbry, 1895) - synonym: ''Pyrgulopsis olivacea'' (Pilsbry, 1895) - olive marstonia, it may be extinct* ''Marstonia ozarkensis'' (Hinkley, 1915) - synonym: ''Pyrgulopsis ozarkensis'' Hinkley, 1915 - Ozark pyrg, it may be extinct* ''Marstonia pachyta'' F. G. Thompson, 1977 - synonym: ''Pyrgulopsis pachyta'' (F. G. Thompson, 1977) - armored marstonia* ''Marstonia scalariformis'' (Wolf, 1869) - synonym: ''Pyrgulopsis scalariformis'' (Wolf, 1869) - moss pyrgOther species of ''Marstonia'' include:* ''Marstonia angulobasis''  F. G. Thompson, 2005 - Angled Marstonia* ''Marstonia comalensis'' (Pilsbry & Ferriss, 1906) - Comal Siltsnail* ''Marstonia gaddisorum'' F. G. Thompson, 2004 - Gaddis Marstonia* ''Marstonia inflata'' H.-J. Wang, 1977 Although ''Marstonia'' has been reviewed four times since 1978 (Thompson 1978, Hershler 1994, Thompson & Hershler 2002, Hershler & Liu 2011), three of its congeners have been little studied beyond their original descriptions and their anatomy is unknown. Two of these — ''Marstonia olivacea'', ''Marstonia ozarkensis'' — may be extinct and thus will likely remain incertae sedis.
References This article incorporates CC-BY-3.0 text from the reference
Further reading * Thompson F. G. & Hershler R. (2002). "Two genera of North American freshwater snails: ''Marstonia'' Baker, 1926, resurrected to generic status, and ''Floridobia'', new genus (Prosobranchia: Hydrobiidae: Nymphophilinae)." ''The Veliger'' '''45'''(3): 269–271.