> Habitat & Distribution

Somatogyrus virginicus populations are widespread in rivers and streams of good flow throughout the southern Atlantic piedmont, extending from the base of the Blue Ridge to the edge of the coastal plain.  But the patchiness of their modern distribution, especially in Virginia and South Carolina, suggests that the range of Somatogyrus may have been significantly impacted by siltation from historic agricultural practices.

A trans-Appalachian population of S. virginicus inhabits the Hiwassee River together with trans-Appalachian Pleurocera catenaria in Polk County, Tennessee.

Solid substrate seems to be a key habitat requirement.  The snail is typically found in rocky riffles with good flow, often associated with the macrophyte Podostemum. FWGNA incidence rank I-4.

> Ecology & Life History

Hydrobiids 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.  We are unaware of any good study on any aspect the biology of Somatogyrus.

> 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.

Somatogyrus virginicus was originally described from the Rapidan River in Virginia, and for many years believed endemic to that particular river system.  It has recently become clear, however, that S. virginicus ranges through southern Atlantic drainages into Georgia (Watson 2000), but that it has been confused with other hydrobiid genera and repeatedly rediscribed under other specific nomena.  Synonyms include georgianus (Walker 1904), tenax (Thompson 1969), alcoviensis (Krieger 1972), and perhaps rheophilus (Thompson 1984) among others. 

> Maps and Supplementary Resources

• Lithoglyphid distribution in Atlantic drainages (2023)
• Somatogyrus distribution in the Tennessee/Cumberland (2022)
• Virginia species account with county distribution (2011)

> Essays

• My post to the FWGNA blog of 26May04, Somatogyrus in the Southeast, included a habitat photo and a figure comparing Somatogyrus to Amnicola, Lyogyrus, and Gillia.
• The 1904 description of Somatogyrus virginicus was touched upon in my 9Nov12 essay reviewing the life and work of Bryant Walker, "Bryant Walker's Sense of Fairness."
• 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, Michigan.  365 pp.
Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom.  509 pp.
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.  
Krieger, K. A. (1972)  Somatogyrus alcoviensis, a new gastropod species from Georgia (Hydrobiidae).  Nautilus 85: 120 – 125.  
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.  
Watson, C. (2000) Results of a survey for selected species of Hydrobiidae (Gastropoda) in Georgia and Florida.  In Freshwater Mollusk Symposia Proceedings, Part II, eds. Tankersley, Warmolts, Watters, Armitage, Johnson & Butler, pp. 233 - 244.  Columbus: Ohio Biological Survey.
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.