> Habitat & Distribution

Ferrissia fragilis ranges throughout North America from southern Ontario to southern California, on rocks, woody debris, macrophytes, and dead leaves in aquatic habitats of all descriptions (Basch 1963, Clarke 1981).  Some minimum levels of dissolved oxygen seem to be required.  Thus populations of F. fragilis are not typically found in warm reservoirs or stagnant waters, or in water that is artificially enriched or polluted.

> Ecology & Life History

Ancylids are generally found to be grazers, with diets especially rich in diatoms (Dillon 2000: 77-79).  Blinn et al. (1989) confirmed the importance of diatoms in the diet of a Ferrissia fragilis population inhabiting a pond in Arizona.

Generation times of less than six weeks have been documented in laboratory populations of F. fragilis, adults maturing around 2-3.0 mm shell length, laying singleton eggs perhaps 0.6 mm in diameter (Dillon & Herman 2009).  Jokinen (1985) reported three generations per year for an F. fragilis population in Connecticut (Life cycle Esis of Dillon 2000:159).  The statewide distribution of F. fragilis documented by Jokinen (1983) suggested to Dillon (2000: 360-363) that the species might show Stress-tolerant life history adaptation.

The allozyme data of Dillon & Herman (2009) suggested that South Carolina populations of F. fragilis are obligately self-fertilizing.  Self-fertilization has also been well-documented in the European freshwater limpet Ancylus fluviatilis (Stadler et al. 1995).

> Taxonomy & Systematics

Basch (1963) recognized five species in the genus Ferrissia - F. rivularis from stones, F. fragilis from vegetation and organic debris in flowing water, F. parallela on narrow-bladed plants in lentic environments, F. walkeri on broad-leaved plants in lentic environments, and F. mcneilli endemic to Alabama.  The shell morphological criteria upon which his system was largely based seem to be subject to a great deal of ecophenotypic plasticity, however (Russell-Hunter et al. 1967, Dillon & Herman 2009).  Walther et al. (2010) combined Basch's five taxa into two species, subsuming parallela under rivularis and walkeri and mcneilli under fragilis.  Ferrissia hendersoni is an older synonym of fragilis as well.

> Supplementary Resources

• Ferrissia distribution in eastern Tennessee River drainages [PDF]
• Virginia species account with county distribution [PDF]

> Essays 

• I reviewed the research findings of Andrea Walther and her colleagues suggesting that North America is inhabited by Two Species of Ferrissia on 8Dec10.  The essay includes a couple nice figures comparing rivularis with fragilis.

> References

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.   
Burky, A. (1971)  Biomass turnover, respiration, and interpopulation variation in the stream limpet Ferrissia rivularis (Say). Ecol. Monog., 41: 235-251.  
Coffman, W. (1971)  Energy flow in a woodland stream ecosystem: I. Tissue support trophic structure of the autumnal community. Arch. Hydrobiol., 68: 232-276.  
Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs.  Cambridge University Press, United Kingdom.  509 pp.  
Dillon, R. T., & J. J. Herman (2009)  Genetics, shell morphology, and life history of the freshwater pulmonate limpets Ferrissia rivularis and Ferrissia fragilis.  J. Freshwat. Ecol. 24: 261 - 271.  [PDF]
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.  
Jokinen, E.  (1983)  The freshwater snails of Connecticut. Hartford, Connecticut, State Geol. Nat. Hist. Survey Bull. 109. 83 p.  
Jokinen, E.  (1985)  Comparative life history patterns within a littoral zone snail community. Verh. Internat. Verein, Limnol., 22: 3292-3399.   
Keating, S.T. & Prezant, R.S. (1998)  Effects of stream chemistry on the distribution, growth, and diatom colonization of the freshwater limpet, Ferrissia rivularis.  J. Freshwat. Ecol. 13: 67-77.  
Russell-Hunter, W.D., M. L. Apley, A. J. Burky, & R. T. Meadows (1967)  Interpopulation variations in calcium metabolism in the stream limpet, Ferrissia rivularis (Say)  Science 155: 338-340.  
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.   
Walther, A. C., T. Lee, J. B. Burch, and D. O'Foighil (2006)  Confirmation that the North American ancylid Ferrissia fragilis (Tryon 1863) is a cryptic invader of European and East Asian freshwater ecosystems.  J. Moll. Stud. 72: 318 - 321.