> Habitat & Distribution

The typical form of Somatogyrus currierianus was described from Huntsville, Alabama, and considered for many years to be a North Alabama endemic.  Our more recent, broader understanding of the taxonomy of these enigmatic little snails suggests that currierianus is the oldest name for populations of Somatogyrus widely distributed throughout river tributaries of the Tennessee, from the Clinch and Powell of the east through North Alabama to the Duck River of middle Tennessee, extending to the Harpeth River west of Nashville.  In previous versions of this web resource we identified East Tennessee populations as "Somatogyrus parvulus."

Throughout its range, populations of S. currierianus currierianus typically reach maximum abundance in rocky riffles.  They are never found on soft bottoms.  FWGNA incidence rank for both subspecies combined I-3.

> Ecology & Life History

Hydrobioid snails seem to be rather nonspecific grazers of small particles (Dillon 2000: 94-97).  They are typically dioecious, the males being characterized by a penis that arises from the neck.  Eggs are generally laid singly, attached in a spare capsule to a solid substrate. 

> Taxonomy & Systematics

Somatogyrus was proposed by Gill (1863) to divide out a subset of Amnicola "with the body whorl globose, and the aperture obliquely semicircular," offering Somatogyrus depressus (Tryon 1862) from the banks of the Mississippi River as the type of the genus.  The lithoglyphine penial morphology, characterized by a simple, unlobed penis with just the single duct, was described subsequently.  Burch followed Thiele in dividing Somatogyrus into two subgenera (Walkerilla and Somatogyrus s.s.) but later opinions suggest little basis for the distinction (Thompson 1984).

Previous versions of this website followed Kabat & Hershler (1993) in recognizing the lithoglyphines as a subfamily in the large, inclusive Hydrobiidae (sl).  More recent molecular phylogenetic evidence has suggested raising this group to the full family level, Lithoglyphidae (Wilke et al., 2013).  See my essay of 18Aug16 from the link below.

Isaac Lea's (1863) "Amnicola currieriana" is the oldest Tennessee/Cumberland nomen for any hydrobioid population subsequently assigned to Somatogyrus.  See the pair of essays I published in 2023 from the links below for the rationale underlying our suggestion that all Tennessee nomina of Somatogyrus be united under it.  We also suggested at the time that more lightly-shelled populations, previously assigned to the genus Clappia, are best understood as a subspecies Somatogyrus currierianus umbilicata.  Junior synonyms include aureus Tryon 1865, excavatus Walker 1906, humerosus Walker 1906, parvulus Tryon 1865, quadratus Walker 1906, sargenti Pilsbry 1895, strengi Pilsbry & Walker 1906, substriatus Walker 1906, and tennesseensis Walker 1906.

> Maps and Supplementary Resources

• Somatogyrus distribution in the Tennessee/Cumberland (2022)

> Essays

• The taxonomy of the North American genus Somatogyrus was a sub-theme of my 9Nov12 post to the FWGNA blog, "Bryant Walker's Sense of Fairness."
• See my essay of 11July23, Somatogyrus and Yankees in North Alabama, for a review of the complicated taxonomic history of lithoglyphine hydrobioid populations in drainages of the Tennessee/Cumberland. That essay features figures of anatomy and shell morphological variation in the genus Somatogyrus.
• In my essay of 15Aug23, The Union in Tennessee, for lithoglyphid hydrobioids, that is, I present evidence that all the Somatogyrus populations of the Tennessee/Cumberland be united under Isaac Lea's nomen, Somatogyrus currierianus, and that populations previously identified as Clappia umbilicata be lowered to subspecific status underneath it.
• Earlier versions of this website, online until August of 2016, adopted the large, broadly-inclusive concept of the Hydrobiidae (sl) following Kabat & Hershler (1993).  More recently the FWGNA project has shifted to the Wilke et al. (2013) classification system, distinguishing a much smaller Hydrobiidae (ss) and elevating many hydrobioid taxa previously ranked as subfamilies to the full family level.  For more details, see The Classification of the Hydrobioids.

> References

Burch, J. B. (1989)  North American Freshwater Snails.  Malacological Publications, Hamburg, MI. 365 pp.
Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom.
Gill, T. (1863)  Systematic arrangement of the mollusks of the family Viviparidae, and others, inhabiting the United States.  Proceedings of the Academy of Natural Sciences of Philadelphia 15: 33 - 40.
Kabat, A.R., and R. Hershler (1993) The prosobranch snail family Hydrobiidae (Gastropoda: Rissooidea): review of classification and supraspecific taxa. Smithsonian Contributions to Zoology 547:1-94. 
Lea, I (1863) Descriptions of fourteen new species of Melanidae and one Paludina.  Proceedings of the Academy of Natural Sciences of Philadelphia 4: 154 – 156.
Lea, I (1866)  New Unionidae, Melanidae, etc., chiefly of the United States.  Journal of the Academy of Natural Sciences of Philadelphia Series 2, 6: 113 – 187.
Thompson, F. (1969) Some hydrobiid snails from Georgia and Florida.  Quart. J. Florida Acad. Sci. 32: 241-65. 
Thompson, F. (1984) North American freshwater snail genera of the hydrobiid subfamily Lithoglyphinae.  Malacologia 25: 109-141.
Walker, B.  (1904)  New species of Somatogyrus.  Nautilus 17: 133-142.
Wilke T., Haase M., Hershler R., Liu H-P., Misof B., Ponder W. (2013)  Pushing short DNA fragments to the limit: Phylogenetic relationships of “hydrobioid” gastropods (Caenogastropoda: Rissooidea).  Molecular Phylogenetics and Evolution 66: 715 – 736.