FWGNA > Species Accounts > Lithoglyphidae > Somatogyrus parvulus
Somatogyrus parvulus Tryon 1865

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> Habitat & Distribution

This is an obscure species, originally described from the Powell River in 1865 and appearing in the literature perhaps only once or twice subsequently.  Walker (1904) reidentified some specimens from a Coosa tributary in Georgia that Isaac Lea considered Somatogyrus aureus to be S. parvulus.  But Walker seems not to have mentioned parvulus in any of his many subsequent papers on the hydrobiids of Tennessee or elsewhere.

We have discovered small populations of S. parvus at two sites on the Powell River - one in Lee County, VA, and a second just over the state line in Claiborne Co, TN.  In both places the snails seem to prefer rocky riffles near midstream.

> 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.  I am unaware of any good study on any aspect the biology of Somatogyrus.

> Taxonomy & Systematics

Males of the genus Somatogyrus bear simple verges, with a single duct, and are thus classified in the hydrobioid family Lithoglyphidae.  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).  The 35 species tallied by Burch doubtless include many synonyms.

> Supplementary Resources

> 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."
  • I published a helpful figure comparing S. parvulus to Amnicola, Clappia, and juvenile Leptoxis in my post of 3Dec12, "On Getting Clappia in Tennessee."
  • 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.
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. 
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.