> Goniobasis semicarinata (Say 1829)
    "Elimia" semicarinata

> Habitat & Distribution
The range of G. semicarinata was given by Goodrich (1940) as "tributaries of Ohio River, Scioto River, Ohio, to Big Blue River, Indiana; Licking River to Salt River in Kentucky; two creeks of Green River of Kentucky."  He apparently did not realize that the species extends up the New River drainage into southern Virginia, down the Blue Ridge scarp to tributaries of the upper Roanoke River, and then up the Great Valley of Virginia through tributaries of the James and the Shenandoah.  Its northernmost limit is in the vicinity of Waynesboro.  Throughout this extensive range G. semicarinata inhabits small, rich, hardwater creeks with rocky bottoms and good flow.

> 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).  

> Taxonomy & Systematics
Three populations of G. semicarinata were included in the allozyme study of Dillon & Davis (1980) - two from tributaries of the upper New River and one from a tributary of the North Fork Roanoke.  The species is quite genetically distinct from G. proxima and G. simplex, two other species that share its range.  Sequence data for the CO1 and 16S mitochondrial genes were published by Dillon & Frankis (2004).  

Burch resurrected the name "Elimia" to include semicarinata 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.

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

 
>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., & G. M. Davis (1980)  The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships.  Malacologia 20: 83-98.  Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp.  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 freshwater snails of the genus Goniobasis Lea, 1862.  Am. Malac. Bull. 19: 69-77.  Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.  Stewart, T. W., & R. T. Dillon, Jr.  (2004)  Species composition and geographic distribution of Virginia's freshwater gastropod fauna: A review using historical records.  Am. Malac. Bull. 19: 79-91.