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Marstonia comalensis
''Marstonia comalensis'' is a species of minute freshwater snail with a gill and an operculum, an aquatic gastropod mollusk or micromollusk in the family Hydrobiidae. It is found in south central Texas, USA.
''Marstonia comalensis'' is large for this genus. It has an ovate-conic, openly umbilicate shell. The penis has a short filament and oblique, squarish lobe bearing a narrow gland along its distal edge.〔 It is well differentiated morphologically from other congeners that have similar shells and penes, and is also genetically divergent relative to those congeners that have been sequenced (mtCOI divergence 3.0–8.5%).〔
This species has often been confused with ''Cincinnatia integra''.〔
== Taxonomy ==
In 1906, Henry Augustus Pilsbry and James Ferriss described this species under the name ''Amnicola comalensis'' based on six shells from Comal Creek and the Guadalupe River near New Braunfels, south-central Texas.〔〔 Pilsbry and Ferriss differentiated this species from ''Amnicola limosa'' (Say) and two nomina (''Amnicola cincinnatiensis'' (), ''Amnicola peracuta'' Pilsbry & Walker) that are currently recognized as synonyms of ''Cincinnatia integra'' (Say) by its much smaller size and noted that it further differed from the latter by its less shouldered whorls.〔 The genus ''Amnicola'' was used at that time as "a catch-all for most American amnicoloid species that could not conveniently be placed elsewhere on the basis of their shells".〔 ''Amnicola comalensis'' was not further treated taxonomically until Taylor (1975)〔 transferred it to ''Cincinnatia'' without comment in a bibliographic compilation;〔 this allocation was widely followed in the subsequent literature.〔 During the course of a revisionary study of ''Cincinnatia integra'', Hershler and Thompson (1996)〔Hershler R. & Thompson F. G. (1996). "Redescription of ''Paludina integra'' Say, 1821, type species of genus ''Cincinnatia'' (Gastropoda: Hydrobiidae)". ''Journal of Molluscan Studies'' 62(1): 33-55. , (PDF ).〕 examined several alcohol preserved collections of a snail that they identified as ''Amnicola comalensis'' and noted that it closely resembled species of ''Marstonia'' (which were then placed in ''Pyrgulopsis''); ''Amnicola comalensis'' was subsequently transferred to ''Marstonia'' based on this unpublished work.〔〔Thompson F. G. & Hershler R. (2002).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)". ''Veliger'' 45: 269-271.〕 Hershler et al. (2003)〔Hershler R., Liu H.-P. & Thompson F. G. (2003). "Phylogenetic relationships of North American nymphophiline gastropods based on mitochondrial DNA sequences". ''Zoologica Scripta'' 32(4): 357-366. .〕 published a molecular phylogenetic analysis of the North American nymphophilines that included a specimen of ''Marstonia comalensis'' from Old Faithful Spring in Real County, Texas (ca. 180 km from the type locality), which was depicted as nested within the ''Marstonia'' clade.〔 This was the only published record for ''Marstonia comalensis'' subsequent to its original description.〔 Hershler & Liu (2011)〔 redescribed ''Marstonia comalensis'' based on study of a large series of dry shell and alcohol-preserved material, most of which was collected by malacologists J. J. Landye and D. W. Taylor from 1971–1993, and provided anatomical evidence supporting its current generic allocation.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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