> Habitat & Distribution
Leptoxis carinata ranges through Atlantic Coastal drainages from the upper Broad River drainage of North Carolina to the upper Susquehanna watershed of New York (Goodrich 1942, Parodiz 1956, Jokinen 1992), as well as into the New River drainage of southern Virginia and northwestern North Carolina (Dillon & Robinson 2009). It also co-occurs with (ecologically similar) Leptoxis praerosa populations in Holston River tributaries draining southwest Virginia and extreme east Tennessee. Within this wide range, populations of L. carinata inhabit streams and rivers with moderate to strong current and abundant rocky substratum (Miller 1985, Stewart and Garcia 2002). FWGNA incidence rank I-5.
Although populations of L. carinata are locally common throughout the Susquehanna drainage of central Pennsylvania, the species does not range into the environmentally-identical Delaware River system, running parallel to the Susquehanna over low ridges immediately to the east. This is by far the most striking example of an effect by river drainage across the entire 85-element freshwater gastropod fauna inhabiting the Atlantic watershed from Georgia to Pennsylvania. Given that the species ranges across seven major watersheds to the south, and indeed over the continental divide into the Ohio and Tennessee systems to the west, limited dispersal capabilities would not seem to offer an adequate explanation. Does the current distribution of Leptoxis carinata in Pennsylvania represent a relict of river drainage patterns as they existed at the Appalachian orogeny? See under "Taxonomy & Systematics" for more.
> Ecology & Life History
& 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 foraging habitat, as well as refuge from high-flow events. In such
environments, Leptoxis carinata densities can
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 epilithic diatoms and other algae, L. carinata can
obtain energy and nutrients through shredding leaves (Dillon &
Davis 1991, Dillon 2000).
Population sex ratios are variable, but tend toward female bias (Cipiaris et al. 2012). Aldridge (1982) and Jokinen (1992) reported semelparous reproduction in northern populations of L. carinata, adults maturing in two years (life cycle Hs of Dillon 2000:156-162), although iteroparous reproduction (Hi) seems more likely in the south. Eggs are deposited on hard substrates in the spring or summer, singly or in masses up to an average of several hundred.
> Taxonomy & Systematics
Parodiz (1956) offered a lovely figure of the shell morphological variation in a single population of L. carinata from the Smith River, Virginia. Such variation has doubtless been responsible for a proliferation of synonyms, which include dissimilis (Say 1819), nickliniana (Lea 1841), variabilis (Lea 1841), and corpulenta (Anthony 1860). Populations inhabiting Holston drainages of the upper Tennessee, referred to the nomen "virgata" by Goodrich (1940), are indistinguishable from L. carinata in our eyes as well. A great variety of generic nomina have also been suggested to contain L. carinata over the years, including Anculosa, Spirodon, Nitocris, and Mudalia (Goodrich 1942, Parodiz 1956).
Dillon & Robinson (2009) nominated L. carinata as one of the "snails the dinosaurs saw," suggesting on the basis of DNA sequence data that populations of these snails may date to the Appalachian orogeny (see my essay of 16Mar09 from the link below.) Their analysis also suggested the nomen Leptoxis dilatata (Conrad 1835), applied for many years to trans-Appalachian Leptoxis populations in the New River, is a junior synonym of L. carinata.
> Supplementary Resources [PDF]
- North Carolina distribution map (2005)
- Leptoxis distribution in eastern Tennessee River drainages (2011)
- Virginia species account with county distribution (2011)
- Leptoxis carinata in the
South Fork Shenandoah River, courtesy of Alan Cressler.
- Pretty photo of living L. carinata,
courtesy of Chris Lukhaup.
- See my FWGNA post of 16Mar09, The Snails The Dinosaurs Saw, for more on the genetics, taxonomy, and distribution of Leptoxis carinata.
D.W. 1982. Reproductive tactics in
relation to life-cycle bioenergetics in three natural populations of
the freshwater snail, Leptoxis carinata. Ecology
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.
Cipiaris, S., W. F. Henley and J. R. Voshell. 2012. Population sex ratios of pleurocerid snails (Leptoxis spp.): Variability and relationshps with environmental contaminants and conditions. Amer. Malac. Bull. 30: 287 - 298.
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.
Goodrich, C. 1940. The Pleuroceridae of the Ohio River drainage system. Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.
Goodrich, C. 1942. The Pleuroceridae of the Atlantic coastal plain. Occas. Pprs. Mus. Zool. Univ. Mich., 456, 1-6.
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.