> Habitat & Distribution

Quoting Basch (1963) verbatim, "Previous records of Rhodacmea place it in the mountain drainages of Kentucky, Tennessee, and Alabama, with populations north into Illinois and Indiana."  Basch went on to remark, however, that he was personally aware of only one popultion alive in his day, that inhabiting Alabama's Cahaba River.  It was Basch's (1963) opinion that "the genus is undoubtably approaching extinction."  We ourselves have confirmed reports of a Rhodacmaea population in the Green River at Munfordville, KY.  We are also aware of a 1987 collection of Rhodacmaea in the Ohio State Museum labelled "Cumberland River at Camp Rowdy" with lat/long coordinates mapping to the Green River about 10 km upstream from Munfordville.  Limpets are found underneath large rocks, about a 1 - 2 feet below summer low water.  FWGNA incidence rank I-1, rare.

> Ecology & Life History

Ancylids are generally found to be grazers, with diets especially rich in diatoms (Dillon 2000: 77-79).  The earliest workers reported that Rhodacmea populations were often found attached to the shells of pleurocerds.  No modern ecological studies have specifically addressed the population biology of Rhodacmea, however.

> Taxonomy & Systematics

Basch (1960) described and figured the anatomy of a Rhodacmea population sampled from the Cahaba River of Alabama.  He observed that "the strangely indented, pink, striated apex, and the peculiar radula distinguish Rhodacmea clearly from all other freshwater limpets."

Walker (1917) described his new genus Rhodacmea (sometimes misspelled "Rhodacmaea") to contain Ancylus filosa (Conrad 1834) of the Mobile Basin, Ancylus eliator (Anthony 1855) from the Green River of Kentucky, Ancylus hinkleyi (Walker 1908) from The Ohio, and three new Mobile Basin species: cahawbensis, rhodacme, and gwatkiniana.  Basch (1963) synonymized Walker's three new species, but kept the three older ones.

The recent study of O'Foighil et al. (2011), demonstrating negligible DNA sequence divergence and negligible shell morphometric difference among two Alabama Rhodacmea populations and one from the Green River of Kentucky, suggests that all American populations be united under the oldest available name, R. filosa (Conrad 1834).   See my essay of 8Aug11 from the link below for a complete review of O'Foighil's (rather controversial) paper.

> Essays 

• I reviewed the research findings of O'Foighil et al. (2011) in my essay of 8Aug11, Rhodacmea Ridotto.  That essay also included additional notes and figures from the influential monograph of Basch (1963).  

> References

Basch, P. (1960) Anatomy of Rhodacmea cahabensis Walker, 1917, a river limpet from Alabama.  The Nautilus 73: 89 - 95.
Basch, P. (1963)  A review of the recent freshwater limpet snails of North America. Bull. Mus. Comp. Zool. Harvard, 129, 399-461. 
Blinn, D., R. Truitt, & A. Pickart. (1989)  Feeding ecology and radular morphology of the freshwater limpet Ferrissia fragilis. J. N. Am. Bentho. Soc., 8: 237-242.   
Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs.  Cambridge University Press, United Kingdom.  509 pp.  
Hubendick, B. (1964) Studies on Ancylidae, The subgroups.  Meddelanden Fran Goteborgs Musei Zoologiska Avendelining, 137.  (Goteborgs Kungl. Vetenskaps-Och Vitterhets-Samhalles Handlingar.  Sjatte Foljden. Ser. B.) 9, 1-72.  
Ó Foighil D, Li J, Lee T, Johnson P, Evans R, Burch JB (2011) Conservation Genetics of a Critically Endangered Limpet Genus and Rediscovery of an Extinct Species. PLoS ONE 6(5): e20496. https://doi.org/10.1371/journal.pone.0020496
Russell-Hunter, W.D., Burky, A.J. & Russell-Hunter, R.D. (1981)  Interpopulaton Variation in Calcareous and Proteinaceous Shell Components in the Stream Limpet, Ferrissia rivularis.  Malacologia 20: 255-266.  
Stadler, T., S. Weisner, & B. Streit (1995) Outcrossing rates and correlated matings in a predominantly selfing freshwater snail.  Proc. R. Soc. Lond. B 262: 119-125.
Walther, A. C., J. B. Burch and D. O’Foighil (2010)  Molecular phylogenetic revision of the freshwater limpet genus Ferrissia (Planorbidae:Ancylinae) in North America yields two species: Ferrissia (Ferrissia) rivularis and Ferrissia (Kincaidilla) fragilis.  Malacologia 53: 25-45.   
Walker, B. (1903)  Notes on eastern American ancyli.  Nautilus 17: 13 - 19, 25 - 31.
Walker, B. (1917)  A revision of the classification of the North American patelliform Ancylidae, with descriptions of new species.  The Nautilus 31: 1 - 10.