> Goniobasis proxima (Say 1825)
    "Elimia" proxima

> Habitat & Distribution
G. proxima ranges in the mountains and piedmont from southern Virginia to north Georgia, primarily in Atlantic drainages but also in the upper New River drainage of the Ohio system and many eastern tributaries of the Tennessee River as well (e.g., upper Nolichucky, upper French Broad / Little Tennessee).  It reaches maximum abundance in smaller streams with high percent groundwater and good flow over rock & cobble substrate (Foin & Stiven 1970, Foin 1971).  Water quality is typically soft and low in nutrients.  Our data show G. proxima not uncommon in high quality, well-oxygenated creeks and rivers of the Piedmont and Blue Ridge ecoregions (Dillon & Keferl 2000).

> Ecology & Life history
Grazing by populations of pleurocerids can have a significant effect on energy flow in small streams (Dillon 2000: 86 - 91, see also Dillon & Davis 1991).   The streams typically inhabited by G. proxima are much poorer in nutrients than those inhabited by any other South Carolina gastropod, but are quite stable and predictable.  The snail populations are perennial and iteroparous, two years being required for maturity (Stiven & Walton 1967, cycle G of Dillon 2000: 156 - 162).  I am not aware of any detailed data on reproductive energetics, but it seems quite likely to me that G. proxima populations are S-adapted in the sense of Dillon (2000: 131- 136).  

The sex ratio seems balanced in some G. proxima populations (Dillon 2000: 104 – 106) although female-biased in others.  Individual movement seems to average around 10 m/yr upstream and 5 m/yr down, but apparently minor barriers may have significant effects (Crutchfield 1966, Dillon 1988a, 1988b, Stiven & Kreiser 1994).  Populations of G. proxima often carry high loads of trematode parasites (Lang 1968).

> Taxonomy & Systematics
The high levels of interpopulation divergence in morphology, allozyme frequency, and DNA sequence are well-documented (Dillon 1984a, 1984b, 1986, Dillon & Reed 2002, Dillon & Frankis 2004, Dillon & Robinson in review).  Dillon & Davis (1980) recognized three races: Race A being the typical form found in the mountains and foothills, Race B inhabiting harder waters, and Race C inhabiting streams of lower flow in the eastern piedmont.  All the SC populations appear to be typical race-A.  Goniobasis symmetrica (Haldeman 1841) is a synonym. The diploid number is 2N = 34 (Dillon 1991).

Burch resurrected the name "Elimia" to include proxima and approximately 80 other pleurocerid species traditionally assigned to Goniobasis (Lea 1862).  But Elimia (H. & A. Adams 1854) is a composite group, explicitly rejected by Tryon, Walker, Pilsbry and Goodrich (Dillon 1989).  Details are available from the link below.

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

>Photo
G. proxima grazing on a wet rock, midstream.

>Pretty photo
Living G. proxima, courtesy of Chris Lukhaup.

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



North Carolina (PDF)

South Carolina (PDF)

Georgia (PDF)

>References
Crutchfield, P. (1966)  Positive rheotaxis in Goniobasis proxima. Nautilus, 79: 80-86.  Dillon, R. T., Jr.  (1984a)  Geographic distance, environmental difference, and divergence between isolated populations. Syst. Zool., 33: 69-82.  Dillon, R. T., Jr.  (1984b)  What shall I measure on my snails?  Allozyme data and multivariate analysis used to reduce the non-genetic component of morphological variance in Goniobasis proxima. Malacologia, 25: 503-511.  Dillon, R. T., Jr. (1986)  Inheritance of isozyme phenotype at three loci in the freshwater snail, Goniobasis proxima: Mother-offspring analysis and an artificial introduction. Biochem. Genet., 24: 281-290.  Dillon, R., T., Jr. (1988a)  Evolution from transplants between genetically distinct populations of freshwater snails. Genetica, 76: 111-119.  Dillon, R. T., Jr. (1988b)  Minor human disturbance influences biochemical variation in a population of freshwater snails. Biol. Conserv., 43: 137-144.  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. (1991)  Karyotypic evolution in pleurocerid snails: II. Pleurocera, Goniobasis, and Juga. Malacologia, 33: 339-344.  Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp.  Dillon, R. T., Jr. & Davis, G. M. (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia, 20, 83-98.  Dillon, R., T. Jr., & K. B. Davis. (1991)  The diatoms ingested by freshwater snails: temporal, spatial, and interspecific variation. Hydrobiologia, 210: 233-242.  Dillon, R., T, Jr., & R. C. Frankis (2004)  High levels of mitochondrial DNA sequence divergence in isolated populations of the freshwater snail genus Goniobasis. Amer. Malac. Bull., 19: 69-77.  Dillon, R. T., Jr. & Keferl, E. (2000) A survey of the pleurocerid gastropods of South Carolina.  In Freshwater Mollusk Symposia Proceedings, Part II, eds. Tankersley, Warmolts, Watters, Armitage, Johnson & Butler, pp. 153 - 160.  Columbus: Ohio Biological Survey.  Dillon, R. & Reed, A. (2002) A survey of genetic variation at allozyme loci among Goniobasis populations inhabiting Atlantic drainages of the Carolinas.  Malacologia 44: 23 - 31.  Dillon, R. & Robinson, J. D. (in review) Genetic relationships among populations of Goniobasis ("Elimia") from central Georgia.  Foin, T. C. (1971)  The distribution pattern of the freshwater prosobranch gastropod Oxytrema proxima (Say). J. Elisha Mitchell Sci. Society, 87: 1-10.  Foin, T.C. & A. Stiven  (1970)  The relationship of environment size and population parameters in Oxytrema proxima (Say) (Gastropoda: Pleuroceridae). Oecologia (Berl.), 5: 74-84.  Goodrich, C. (1942) The Pleuroceridae of the Atlantic coastal plain. Occas. Pprs. Mus. Zool. Univ. Mich., 456, 1-6.  Lang, B. Z. (1968)  Note on ecology of Goniobasis proxima in North Carolina.  Nautilus 82: 3 – 5.  Stiven, A. E. & B.R. Kreiser (1994)  Ecological and genetic differentiation among populations of the gastropod Goniobasis proxima (Say) in streams separated by a reservoir in the piedmont of North Carolina.  J. Elisha Mitchell Sci. Society 110: 53 – 67.  Stiven, A., & C. Walton. (1967)  Age and shell growth in the freshwater snail, Goniobasis proxima (Say). Am. Midl. Natur., 78: 207-214.