> Habitat & Distribution

Lyogyrus granum ranges throughout eastern North America from Florida to the Hudson Bay, as far west as Wisconsin (Baker 1928, Clarke 1981, Thompson 1999).  We have widespread records through almost all Atlantic drainages, typically in impoundments and river backwaters of the lower Piedmont and Coastal Plain in the South, ponds and lakes in the North. Populations are surprisingly rare further west, however.  We have only a few very scattered records from any tributary of The Ohio.  FWGNA incidence rank I-5.

> Ecology & Life History

The dynamics of Lyogyrus granum populations seem unusually “flashy,” especially for a prosobranch.  Although we have several years of observations at the Salkehatchie River east of Yemassee, SC, without a single record, for example, in March of 2004 Lyogyrus suddenly became the most common gastropod at that site.  Jokinen (1983) reported an annual life cycle for a population inhabiting a Connecticut pond (type A of Dillon 2000: 156 – 162).

Jokinen's (1987) analysis of the distribution of L. granum in Connecticut and New York led her to classify it as a “High-S” species, found only in the most species-rich communities.  Dillon’s (2000: 360-363) reanalysis of these data suggested that L. granum populations in Connecticut might be S-adapted, common in poor but stable environments, demonstrating low reproductive effort relative to body size.

> Taxonomy & Systematics

Lyogyrus is a member of the hydrobioid family Amnicolidae, characterized by a doubly-ducted penial morphology (Hershler & Thompson 1988).  Of the two amnicolid genera inhabiting the study area, Lyogyrus is distinguished by an operculum that is initially multispiral, becoming paucispiral in adult individuals.  See my essay of 26May04 from the link below.

Through most of the 20th century, Lyogyrus (Gill 1863) was treated as a subgenus of Amnicola, but Thompson & Hershler (1991) raised it back to full generic rank.  Synonyms of L. granum include pupoidea (Gould 1841) and walkeri (Pilsbry 1898) in the north and retromargo (Thompson 1968) in the south.

> Maps and Supplementary Resources

• Lyogyrus distribution in drainages of The Ohio (2019)
• Amnicolid distribution in Atlantic drainages (2023)
• Distribution in the Tennessee/Cumberland (2022)
• Virginia species account with county distribution

> Essays

• My post to the FWGNA blog of 26May04, Somatogyrus in the Southeast, also included notes on Lyogyrus and a nice comparative photo.
• 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

Baker, F. C. (1928) The Freshwater Mollusca of Wisconsin. Part 1, Gastropoda.  Bull. Wisc. Geol. Natur. Hist. Survey, no. 70. Madison: University of Wisconsin Press.
Clarke, A. H. (1981) The Freshwater Molluscs of Canada.  National Museums of Canada, Ottawa.  446 pp.
Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom.  509 pp.
Hershler, R. & Thompson, F. G. (1988) Notes on morphology of Amnicola limosa (Say), with comments on status of the subfamily Amnicolinae.  Malac. Rev. 21: 81-92.
Jokinen, E. H. (1983)  The freshwater snails of Connecticut.  State Dept of Environmental Protection Bulletin 109, 83 pp.
Jokinen, E. (1987) Structure of freshwater snail communities: Species-area relationships and incidence categories.  Amer. Malac. Bull. 5: 9 - 19.
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. G. (1968)  The aquatic snails of the family Hydrobiidae of peninsular Florida.  University of Florida Press, Gainesville.  268 pp.
Thompson, F. G. (1999)  An identification manual for the freshwater snails of Florida. Walkerana 10: 1-96.
Thompson, F. G. & R. Hershler (1991)  Two new hydrobiid snails (Amnicolinae) from Florida and Georgia, with a discussion of the biogeography of freshwater gastropods of south Georgia streams.  Malac. Rev. 24: 55-72.
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.