> Goniobasis catenaria dislocata (Ravenel 1834)
    "Elimia" catenaria dislocata

> Habitat & distribution
Populations of this G. catenaria subspecies seem restricted to an unusual habitat: streams and small rivers of high groundwater content and good flow in the Southeastern Plains Ecoregion.  Like typical G. catenaria catenaria, dislocata is not found in acidic waters, and seems positively associated with limestone.  But it does not seem as strict in its requirement of rocky substrate, and can be found on bottoms of firm sand and woody debris.  Its distribution in our study area is spotty, being recorded from several eastern North Carolina counties and Greensville County, Va, by Goodrich (1942) as well as from scattered South Carolina counties by Dillon & Keferl (2000).  It seems to reach its southern limit in Georgia tributaries of the Ogeechee River. 

> Ecology & Life history
Although I am unaware of any ecological study directed specifically toward G. catenaria dislocata, I imagine the outline of its life history is similar to that of G. catenaria catenaria.  Dislocata populations may reach high densities in smaller streams (e.g., cave springs flowing east into Lake Marion) and hence might be more likely to impact energy flow than typical catenaria.

> Taxonomy & Systematics
Superficially this species is distinguishable from G. proxima only by the presence of faint costae on the apical whorls.  But allozyme frequencies confirm a close genetic similarity to G. catenaria catenaria (Dillon & Reed 2002).  The striking reduction in shell sculpture displayed by dislocata may be a phenotypically-plastic response to soft substrate or some other peculiar aspect of their environment, as has been documented in Japanese Semisulcospira populations by Urabe (1998, 2000).

I (and many others) have previously attributed the specific nomen "dislocata" to Reeve, when in fact the correct author was Ravenel (1834).  In any case, Goodrich (1942) was the first to lower the name to subspecific rank, a judgement wisely followed by Burch.  The promotion of dislocata back to the full species level by Turgeon et al. (1998) was neither justified nor justifiable.

The diploid number is 2N = 34 (Dillon 1991).  Mitochondrial CO1 and 16S sequence data are available in Dillon & Frankis (2004).

Burch resurrected the name "Elimia" to include dislocata 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.

>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
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. & 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., 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. & Reed, A. (2002) A survey of genetic variation at allozyme loci among Goniobasis populations inhabiting Atlantic drainages of the Carolinas.  Malacologia 44: 23 - 31.  Goodrich, C. (1942) The Pleuroceridae of the Atlantic coastal plain. Occas. Pprs. Mus. Zool. Univ. Mich., 456, 1-6.   Turgeon, D. D. et al. (1998) Common and scientific names of mollusks, second edition.  American Fisheries Society Sp. Publ. 26.  Urabe, M. (1998)  Contribution of genetic and environmental factors to shell shape variation in the lotic snail Semisulcospira reiniana (Prosobranchia: Pleuroceridae). J. Moll. Stud., 64: 329-343.  Urabe, M.  (2000)  Phenotypic modulation by the substratum of shell sculpture in Semisulcospira reiniana (Prosobranchia: Pleuroceridae). J. Moll. Stud., 66: 53-60.