> Goniobasis virginica (Say 1817)
    ("Elimia virginica")

> Habitat & Distribution
Populations of this species are widespread in Atlantic coastal drainages, ranging from Connecticut and Massachusetts to North Carolina, and as far west as central New York State (Burch 1989, Jokinen 1992, Harman 2000, Stewart and Dillon 2004). Goniobasis virginica is common in large rivers, and occasionally occurs in smaller streams and lakes. Rock and other hard substrata are preferred habitat, but individuals can be found on soft substrata and vegetation (Harman 1972, Jokinen 1992).

> Ecology & Life history
This and other pleurocerids are grazers of epilithic periphyton (Harman 2000). Where they reach high densities, grazing by pleurocerid populations can have a significant effect on energy flow in streams (Dillon 2000: 86 - 91). Habitat degradation caused declines and local extinctions of stream- and lake-dwelling Goniobasis virginica populations in the northeastern United States during the 20th century (Smith 1980, Harman 2000).

Like other pleurocerids, G. virginica is dioecious, eggs being deposited on hard substrates from spring to mid-summer. Eggs are spirally arranged in masses of 2-15 or more, with a tough, membranous outer covering (Smith 1980, Jokinen 1992). Although we are unaware of any study specifically directed toward the life history of G. virginica, it seems reasonable to expect that two years will be required for maturity, and that several years of iteroparous reproduction can be expected thereafter, as is the case for pleurocerids generally (Dazo 1965). This is life cycle G of Dillon (2000: 156 - 162).

> Taxonomy & Systematics
Bianchi et al. (1994) used allozyme data to document a hybrid zone between G. virginica and G. livescens of the American interior, apparently promoted by the opening of the Erie Canal.  Holznagel & Lydeard (2000) reported sequence data from the 16S rRNA gene of an individual sampled from Pennsylvania.

Burch (1989) and Turgeon et al. (1998) assigned this species to the genus Elimia. But Elimia (H. & A. Adams 1854) is a composite group, explicitly rejected by Tryon, Walker, Pilsbry and Goodrich (Dillon 1989).

> Essay
See my 28Sept04 post to the FWGNA web site for a review of the Goniobasis/Elimia taxonomic controversy.

> Photomontage
living G. virginica, courtesy of Bill Zeller.

>Map of Goniobasis distribution
Click the small map to enlarge it, or download the state-specific PDF



North Carolina (PDF)

>References
Bianchi, T. S., G. M. Davis, and D. Strayer 1994.  An apparent hybrid zone between freshwater gastropod species Elimia livescens and E. virginica (Gastropoda: Pleuroceridae).  Am. Malac. Bull. 11: 73 - 78.  Burch, J.B. 1989. North American Freshwater Snails. Malacological Publications, Hamburg, Michigan. Dazo, B. C. 1965. The morphology and natural history of Pleurocera acuta and Goniobasis livescens (Gastropoda: Cerithiacea: Pleuroceridae). Malacologia 3: 1 - 80. Dillon, R., T. Jr. 1989. Karyotypic evolution in pleurocerid snails: I. Genomic DNA estimated by flow cytometry. Malacologia, 31: 197-203. Dillon, R.T., Jr. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom. Harman, W.N. 1972. Benthic substrates: their effect on fresh-water Mollusca. Ecology 53: 271-277. Harman, W.N. 2000. Diminishing species richness of mollusks in Oneida Lake, New York State, USA. Nautilus 114:120-126.  Holznagel, W. E. & C. Lydeard 2000.  A molecular pylogeny of North American Pleuroceridae (Gastropoda: Cerithioidea) based on mitochondrial 16S rDNA sequences.  J. Moll. Stud. 66: 233 - 257.   Jokinen, E.H. 1992. The Freshwater Snails (Mollusca: Gastropoda) of New York State. NY State Mus Bull 482, Albany, New York. Smith, D.G. 1980. Goniobasis virginica Gastropoda Pleuroceridae in the Connecticut River USA. Nautilus 94:50-54. 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. Turgeon, D.D. et al. 1998. Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Mollusks. Amer Fish Soc Sp Pub 26, Bethesda, Maryland.