> Goniobasis arachnoidea (Anthony 1854)
    "Elimia" arachnoidea

> Habitat & Distribution
The range of G. arachnoidea was given by Goodrich (1940) as "small streams in Tennessee and southwestern Virginia."  Our surveys suggest that the Virginia portion of its range is restricted to tributaries of the Powell River in Lee and western Wise Counties.  Within that region it primarily inhabits small, rich, hardwater creeks.  We have collected G. arachnoidea from Clinch River tributaries in Tennessee, but have not been able to confirm the occurrence of the species in Clinch tributaries north of the Virginia line.  Nor have we been able to confirm the report of G. arachnoidea in Holston tribuataries around Gate City (Goodrich 1913).  

> 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. arachnoidea were included in the allozyme study of Dillon & Robinson (2007a).  The species is quite distinct genetically.  There is no evidence of hybridization with either G. simplex or G. clavaeformis, the other two species of Goniobasis with which it sometimes co-occurs.  Goniobasis spinella (Lea, 1862) is a synonym.

Burch resurrected the name "Elimia" to include arachnoidea 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. arachnoidea, 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. (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.  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.