> Hebetancylus excentricus (Morelet 1851)

> Habitat & Distribution
Basch (1963) gave the range of this limpet as Georgia, Florida and Texas.  My attention was called to the occurrence of Hebetancylus in South Carolina by J. R. Harrison, who discovered a population in a pond on the Dill Plantation south of Charleston several years ago (Harrison 1989).  The pond is frequented by migratory birds, and in fact serves as a study site for ornithologists from the Charleston Museum.  Harrison and I were unable to find the limpet again in late 2004, although high water conditions made collecting difficult.  I have since recorded Hebetancylus populations from two other ponds in the Charleston area, however - Drayton Hall Plantation and Charles Towne Landing State Park.  The limpets seem moderately common on submerged sticks, logs, and large items of organic debris.  I am also aware of three populations in North Carolina, as well as scattered populations in Georgia.

> Ecology & Life history
Turner & Corkum (1979) reported simple annual life cycles in several Louisiana populations of Hebetancylus (type A of Dillon 2000: 156-162), one bivoltine (type C) population and one trivoltine (perhaps Esii).  Other life history observations are available in McMahon (1976).  Harrison (1989) reported that some of the individuals he collected from the Dill Plantation population were septate, suggesting that they may have passed a period of dry or otherwise harsh environmental condition in aestivation.

> Taxonomy & Systematics
The presence of an apex distinctly off midline is generally considered diagnostic for this species.  McMahon (2004) reported, however, that shell shape varied to such an extent in one Oklahoma population of limpets that no positive assignment could be made between Hebetancylus and Laevapex.  Subsequent genetic work showed McMahon's population to be Laevapex (Walther et al. 2006).

> Essay
Hebetancylus figured in a November 2005 essay I posted to the FWGNA group on the aerial dispersal of mollusca.

> Maps of Hebetancylus distribution
Click the small map to enlarge it, or download the state-specific PDFs



North Carolina (PDF)

South Carolina (PDF)

Georgia (PDF)

> References
Basch, P. (1963)  A review of the recent freshwater limpet snails of North America. Bull. Mus. Comp. Zool. Harvard, 129, 399-461.  Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs.  Cambridge University Press, United Kingdom.  509 pp.  Harrison, J. R. (1989)  The freshwater limpet Hebetancylus excentricus (Morelet) in South Carolina (Abstract).  ASB Bulletin 36(2): 110.  McMahon, R. F. (1976)  Growth, reproduction and life cycle in six Texan populations of two species of fresh-water limpets.  Am. Midl. Nat. 95: 174-185.  McMahon, R.F.  (2004) A 15-year study of interannual shell-shape variation in a population of freshwater limpets.  Amer. Malac. Bull. 19:101- 109.  Turner, H. M. & K. C. Corkum (1979)  A seasonal and ecological survey of freshwater limpet snails (Pulmonata: Ancylidae) and their digenetic trematode parasites in southeastern Louisiana.  Tulane Stud. Zool. Bot. 21: 67 – 89.    Walther, A. C., T. Lee, J. B. Burch & D. O'Foighil (2006)  E pluribus unum: A phylogenetic and phylogeographic reassessment of Laevapex (Pulmonata: Ancylidae), a North American genus of freshwater limpets.  Molec. Phyl. Evol. 40: 501 - 516.