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.

[3] 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.

[3] Amnicola comalensis was not further treated taxonomically until Taylor (1975)[2] transferred it to Cincinnatia without comment in a bibliographic compilation;[3] this allocation was widely followed in the subsequent literature.

[3] During the course of a revisionary study of Cincinnatia integra, Hershler and Thompson (1996)[4] 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(which were then placed in Pyrgulopsis); Amnicola comalensis was subsequently transferred to Marstonia based on this unpublished work.

[3][5] Hershler et al. (2003)[6] 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.

[3] Hershler & Liu (2011)[3] 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.

[3] It is possible that Marstonia comalensis became extinct at Comal Springs when this water body temporarily dried in 1964; it is also possible that the shells of this species which have been found at this site were washed downflow from extant populations in the headwaters of the Guadalupe River.

[3] Records published by Hershler & Liu (2011)[3] considerably expanded the geographic range of Marstinia comalensis, which lives in springs and fluvial habitats spread among four river basins in south-central Texas.

[3] Hershler & Liu (2011)[3] were unable to confirm a previous report by Cable & Isserhoff (1969)[7] of this species from a drainage canal near Galveston Bay.

[3] Hershler & Liu (2011)[3] also analyzed previously published molecular data to evaluate the genetic divergence and phylogenetic relationships of Marstonia comalensis, whose geographic range is broadly disjunct relative to other members of the genus.

[3] The sculpture of strong collabral growth lines, later whorls having numerous weak spiral striae.

Reproductive system: Testis is large (1.75 whorls), composed of compound lobes, broadly overlapping stomach anteriorly.

[3] Anterior vas deferens opening from antero-ventral edge of prostate gland, section of duct on columellar muscle straight.

[3] Terminal gland is narrow, usually transversely positioned along outer edge of lobe, less frequently horizontal, sometimes borne on short stalk.

[3] Seminal receptacle is small, pouch-like, positioned near ventral edge of albumen gland slightly anterior to bursa copulatrix.

[3] Marstonia comalensis has a closely similar shell and penis to some of its congeners, but can be differentiated from them in these ways: It can be distinguished from Marstonia gaddisorum by its less convex shell whorls, distinctive pallial roof pigmentation, larger number of cusps on the inner side of the lateral teeth and on the outer marginal teeth, larger penial lobe, narrower terminal gland, and smaller overlap of the bursa copulatrix by the albumen gland.