> Goniobasis simplex (Say 1825)
    "Elimia" simplex

> Habitat & Distribution
The range of G. simplex was given by Goodrich (1940) as "headwaters of Tennessee River system in Virginia, Tennessee and North Carolina; Beaver Fork of Bluestone River of Kanawha River, Mercer County, West Virginia."  The species is indeed common in smaller tributaries of the Clinch, Powell, and Holston Rivers in southwest Virginia, especially in rich, hardwater, spring-fed streams.  It also occurs in several tributaries of the New River just east of the Tennessee divide - Reed Creek in Wythe County, Walker Creek in Giles County, and perhaps elsewhere.

> 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
Two populations of G. simplex were included in the allozyme study of Dillon & Davis (1980) - the Reed Creek population mentioned above and a population from a tributary of the Middle Fork Holston River perhaps 10 km west.  These populations were nearly identical at ten loci.  Five additional populations were surveyed by Dillon & Robinson (2007a), including a sample from the type locality of the species in the North Fork Holston River at Saltville.  The species is quite distinct genetically.  There is no evidence of hybridization with either G. clavaeformis or G. arachnoidea, the other two species of Goniobasis with which it sometimes co-occurs.  Goniobasis aterina (Lea 1863) is a synonym.  

Burch resurrected the name "Elimia" to include simplex 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. simplex, 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 Crolina: 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., & J. D. Robinson (2007a) The Goniobasis ("Elimia") of southwest Virginia, I. Population genetic survey.  Report to the Virginia Division of Game & Inland Fisheries, 25 pp.   Dillon, R. T., Jr., & J. D. Robinson (2006)  Population genetic survey of the genus Goniobasis ("Elimia") in southwest Virginia.  Report to the Virginia Division of Game & Inland Fisheries, 20 pp.  Goodrich, C. (1913)  Spring collecting in southwest Virginia.  Nautilus 27: 81-82, 91-95.  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.