> Habitat & Distribution

Walker (1918) gave the American range of G. altilis as New Jersey to South Carolina.  Thompson (1984) mapped about 50 well-documented records in Atlantic drainages from South Carolina as far north as the Hudson drainage and west to Lake Ontario, suggesting that the Lake Ontario population might have been introduced artificially, through the Erie Canal.   Jokinen (1992) extended the range of G. altilis as far north as Vermont.  Doug Smith (pers. comm.) reported an apparently healthy population of Gillia on the shores of Lake Champlain.

At the southern end of its range, however, G. altilis seems to be rather uncommon.  Its type locality was the Santee Canal, an early nineteenth century passage between Charleston and the Santee River to the north, long defunct and now largely submerged under the waters of Lake Moultrie.  We are aware of only two populations surviving in South Carolina today, in the Lynches River south of Florence, and in a tributary of the Combahee River near Allendale.  Gillia in the Lynches River shows similar habitat preferences to the sparse Pleurocera catenaria population with which it co-occurs, strongly associated with rip rap rocks and hard clay islands in an environment otherwise characterized by mud and sand.  Populations are more widespread in North Carolina, but again quite patchy in Virginia.  It seems likely that the range of the species throughout the southeast may have been severely impacted by erosion and sedimentation.  FWGNA incidence rank I-4.

> Ecology & Life History

We are unaware of any good study on any aspect the biology of Gillia.  But given its association with scattered hard substrates in silty rivers, one might speculate that it is a generalized grazer, like hydrobiids generally (Dillon 2000: 94-97). Hydrobiids are typically dioecious, the males being characterized by a penis that arises from the neck.  Females attach single eggs in spare, hemispherical capsules to solid substrates (Hershler 1994).

> Taxonomy & Systematics

The Hydrobioids are unquestionably the most diverse group of freshwater gastropods in North America, displaying great anatomical as well as conchological variety.  One might think that taxonomists working with a group containing such a vast number of species would tend not to erect monotypic genera, but it seems to us that the opposite is often the case.

The monotypic genus Gillia is characterized by a simple, single-ducted verge, classifying it together with Somatogyrus and several other North American genera in the family Lithoglyphidae. Its anatomy has been described by Thompson (1984).

> Maps and Supplementary Resources

• Lithoglyphid distribution in Atlantic drainages (2023)
• Virginia species account with county distribution (2011)

> Essays

• My post to the FWGNA blog of 26May04, Somatogyrus in the Southeast, included habitat notes on Gillia and a figure comparing Gillia to several other similar hydrobiid taxa.
• See my post of 24Jan05 announcing Gillia rediscovered in South Carolina.  There's also a photo of the critter on the hoof.
• The sad fate of the Waccamaw population of Gillia was mentioned in my post of 16July10, Crisis at Lake Waccamaw.
• 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

Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp. 
Hershler, R. (1994)  A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Smithsonian Contributions to Zoology 0(554):1-115.   
Jokinen, E.  (1992)  The freshwater snails (Mollusca: Gastropoda) of New York State. New York State Museum Bulletin 482: 1-112.  
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. (1984) North American freshwater snail genera of the hydrobiid subfamily Lithoglyphinae.  Malacologia 25: 109-141. 
Walker, B.  (1918)  A Synopsis of the Classification of the Freshwater Mollusca of North America, North of Mexico. Misc. Pubs., vol. 6. Ann Arbor, University of Michigan Press.
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.