> Leptoxis carinata (Brug. 1792)

> Habitat & Distribution
Leptoxis carinata ranges through Atlantic Coastal drainages from New York to North Carolina (Burch 1989, Parodiz 1956, Jokinen 1992), as well as into the New River drainage of southern Virginia and northwestern North Carolina.  Within this wide range populations inhabit streams and rivers with moderate to strong current and abundant rocky substratum (Miller 1985, Stewart and Garcia 2002).

> Ecology & Life history
Stewart & Garcia (2002) reported that topographic complexity of substratum (i.e., rock abundance) was the primary cause of local variation in Leptoxis carinata densities and total biomass in a Virginia piedmont stream. Density and biomass were greatest in topographically complex plots with boulders and cobble that provide ideal foraging habitat for these periphyton scrapers, as well as refuge from high-flow events. In such environments, Leptoxis carinata densities can exceed 500 individuals per square meter, and this species can constitute more than 80% of total macroinvertebrate biomass (Miller 1985; Stewart and Garcia 2002; Stewart and Dillon 2004). In addition to grazing on rock-inhabiting diatoms and other algae, L. carinata can obtain energy and nutrients through shredding leaves (Dillon & Davis 1991, Dillon 2000).

Like all pleurocerids, L. carinata is dioecious.  Aldridge (1982) and Jokinen (1992) reported semelparous reproduction in northern populations, adults maturing in two years (life cycle Hs of Dillon 2000:156-162). Eggs are deposited on hard substrates in the spring or summer, singly or in masses up to an average of 170-400 eggs per female.

> Taxonomy & Systematics
The sequence data of Dillon & Robinson (2009) suggested strongly that the nomen Leptoxis dilatata (Conrad 1835), applied for many years to the Leptoxis populations inhabiting New River drainages in NW North Carolina and western Virginia, is a junior synonym of L. carinata (see the essay of 16Mar09 below.)  Other synonyms include Anculosa carinata, Leptoxis nickliniana, Melania nickliniana, Mudalia carinata, Nitrocris carinata, and Spirodon carinata (Goodrich 1921, Stewart and Dillon 2004).  Parodiz (1956) offered a lovely figure of the shell morphological variation in a single population of L. carinata from Smith River, Virginia.

>Essay
See my FWGNA post of 16Mar09, "The Snails The Dinosaurs Saw," for more on the genetics, taxonomy, and distribution of L. carinata.

>Pretty photo
Living L. carinata, courtesy of Chris Lukhaup.

>Maps of Leptoxis carinata distribution
Click the small map to enlarge it, or download the state-specific PDF



North Carolina (PDF)

>References
Aldridge, D.W. 1982. Reproductive tactics in relation to life-cycle bioenergetics in three natural populations of the freshwater snail, Leptoxis carinata. Ecology 63:196-208. Brown, K.M. 2001. Mollusca: Gastropoda. In: J.H. Thorp and A.P. Covich, eds., Ecology and Classification of North American Freshwater Invertebrates, Academic Press, New York. Pp. 297-329. Burch, J.B. 1989. North American Freshwater Snails. Malacological Publications, Hamburg, Michigan. Dillon, R.T., Jr. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom. Dillon, R.T., and K.B. Davis. 1991. The diatoms ingested by freshwater snails: temporal, spatial, and interspecific variation. Hydrobiologia 210: 233-242.  Dillon, R.T., and J.D. Robinson. 2009.  The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?  J. N. Am. Benthol. Soc. 28: 1-11.  Goodrich, C. 1921. Anculosae north of the Alabama drainage. Nautilus 35:9-12. Jokinen, E.H. 1992. The Freshwater Snails (Mollusca: Gastropoda) of New York State. NY State Mus Bull 482, Albany, New York. Miller, C. 1985. Correlates of habitat favourability for benthic macroinvertebrates at five stream sites in an Appalachian mountain drainage basin, USA. Freshw Biol 15:709-733.  Parodiz, J. J. (1956)  Notes on the freshwater snail Leptoxis (Mudalia) carinata.  Annals of the Carnegie Museum 33: 391 - 405.  Stewart, T.W., and R.T. Dillon, Jr. 2004. Species composition and geographic distribution of Virginia’s freshwater gastropod fauna: a review using historical records. Amer Malac Bull 19:79-91. Stewart, T.W., and J.E. Garcia. 2002. Environmental factors causing local variation in density and biomass of the snail Leptoxis carinata, in Fishpond Creek, Virginia. Amer Midl Natur 148:172-180.