FWGNA > Species Accounts > Pleuroceridae > Pleurocera troostiana
Pleurocera troostiana (Lea 1839)
Goniobasis or "Elimia” arachnoidea
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> Habitat & Distribution

The range of P. troostiana was restricted by Goodrich (1940) to "Mossy Creek, Jefferson County, Tennessee."  Our surveys suggest that together with all its probable synonyms, however, P. troostiana populations are widespread throughout the Unglaciated Interior Low Plateau of Tennessee, central and western Kentucky, extending from the Green River through most of the Cumberland and Tennessee River systems east into tributaries of the Powell River in southwest Virginia.  

Within this region it primarily inhabits small, rich, hardwater creeks and springfed streams.  Populations are also occasionally found in larger rivers when cool and clear, especially when spring sources are nearby.  We have not been able to confirm populations of P. troostiana from Clinch River tributaries north of the Virginia line, nor reports of the species in Holston tribuataries around Gate City (Goodrich 1913).   FWGNA incidence rank I-5.

> 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).

Like other pleurocerids, P. troostiana is dioecious, eggs being deposited on hard substrates from spring to mid-summer. Eggs are spirally arranged in masses of 2-15 or more, with a tough, membranous outer covering to which sand grains typically adhere (Smith 1980, Jokinen 1992). Although we are unaware of any study specifically directed toward the life history of P. troostiana, it seems reasonable to expect that two years will be required for maturity, and that several years of iteroparous reproduction can be expected thereafter, as is the case for pleurocerids generally (Dazo 1965). This is life cycle Hi of Dillon (2000: 156 - 162). 

> Taxonomy & Systematics

In our prior publications (Stewart & Dillon 2004, Dillon & Robinson 2007a) as well as in previous versions of this website, we referred to this species as Pleurocera (or Goniobasis) arachnoidea - the oldest name available in the Virginia literature.  The extension of the FWGNA survey into east Tennessee, however, uncovered a great number of synonyms for this species with older dates than Anthony's (1854) arachnoidea.  These include troostiana (Lea 1839), strigosa (Lea 1841), teres (Lea 1841), and striatula (Lea 1842), as well the subsequent athleta (Anthony 1854), glauca (Anthony 1860) rubella (Lea 1862), spinella (Lea 1862) and porrecta (Lea 1863).

Kentucky populations of this same, highly variable species were referred to Goniobasis (or Elimia) plicata-striata (Wetherby 1876) or curryana (Lea 1841) by Branson (1987), and to Goniobasis curryana lyoni (Lea 1863) by Bickel (1968).  All these pleurocerid taxa differ (at most) in shell striae and other minor aspects of shell sculpture, a variable and possibly ecophenotypic character (Goodrich 1935), and all are junior synonyms of Lea's troostiana.

There is much confusion on the precise date of Lea's authorship, however - Burch giving 1838 and both Tryon and Goodrich giving 1841.  Lea apparently read his paper describing Melania troostiana before the American Philosophical Society on November 4, 1836, but the date on the front cover of Transactions Volume 6 (in which his description was published) states "1839."  Let's go with 1839, shall we?

Three populations of P. troostiana (identified as 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 P. simplex or P. clavaeformis, the other two species of Pleurocera with which it sometimes co-occurs.

This species has travelled through three genera in thirty years.  Although predominantly assigned to Goniobasis through most of the 20th century, in the 1980s many workers began placing it in the resurrected generic nomen, "Elimia."  Both Goniobasis and Elimia were subsumed under Pleurocera by Dillon (2011).  See my essay of 23Mar11 from the link below for more.

> Supplementary Resources

  • Pretty photo of living P. troostiana, courtesy of Chris Lukhaup.Pretty photo

> Essays

  • Taxonomic controversy has surrounded the generic nomina Pleurocera, Goniobasis, and Elimia for many years.  The best entry into the subject would be my essay of 23Mar11, entitled Goodbye Goniobasis, Farewell Elimia.  Links are available from that essay to older resources.

> References

Bickel, D.  (1968)  Goniobasis curreyana lyoni, a pleurocerid snail of west-central Kentucky. The Nautilus 82: 13 - 18.
Branson, B.A. (1987)  Keys to the aquatic gastropoda known from Kentucky.  Trans. Kentucky Acad. Sci. 48: 11 - 19.
Burch, J. B. (1989)  North American Freshwater Snails.  Malacological Publications, Hamburg, Michigan.  365 pp.
Dazo, B. C. (1965)
The morphology and natural history of Pleurocera acuta and Goniobasis livescens (Gastropoda: Cerithiacea: Pleuroceridae). Malacologia 3: 1 - 80. 
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. (2011)  Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque, 1818).  Malacologia 53: 265-277.
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.  [PDF]
Goodrich, C. (1913)  Spring collecting in southwest Virginia.  Nautilus 27: 81-82, 91-95.
Goodrich, C. (1935)  Studies of the gastropod family Pleuroceridae V.  Occas. Pprs. Mus. Zool. Univ. Mich., 318: 1 - 12. 
Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.
Jokinen, E.H. 1992.
The Freshwater Snails (Mollusca: Gastropoda) of New York State. NY State Mus Bull 482, Albany, New York.
Smith, D.G. 1980. Goniobasis virginica (Gastropoda: Pleuroceridae) in the Connecticut River USA. Nautilus 94:50-54.
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.