FWGNA > Species Accounts > Pleuroceridae > Pleurocera ebenum
Pleurocera simplex ebenum (Lea 1841)
Goniobasis or "Elimia” ebenum
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> Habitat & Distribution

Goodrich (1940) restricted the distribution of P. ebenum to the Cumberland River and its tributaries in Kentucky and Tennessee, and Stewart & Dillon did not include the species in their (2004) Virginia review.  But our broader surveys and improved understanding of the taxon have extended the range of pleurocerid populations bearing the ebenum morphology, now recognized as a subspecies of P. simplex, from the Cumberland drainage through the Levista/Big Sandy drainage of KY/VA, the upper regions of the Kentucky River drainage, most of the Green River drainage of KY/TN, and even tributaries of the Duck River in Middle Tennessee.

Throughout this range, populations of P. simplex ebenum typically inhabit rivers and larger streams with rocky substrate and good flow.  Populations inhabiting smaller and perhaps richer streams, bearing darker shells more concave in outline and carinate on the upper whorls, are generally identified as typical P. simplex simplex.  The FWGNA incidence rank of the two subspecies considered together is 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. simplex ebenum 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 (Smith 1980, Jokinen 1992). Although we are unaware of any study specifically directed toward the life history of P. simplex ebenum, 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 versions of this website prior to 2017, the FWGNA project followed Goodrich and all previous workers in according Lea's (1841) nomen ebenum full specific status.  But our more recent explorations in the Cumberland, Kentucky, and Green River drainages flowing west to the Ohio have returned evidence that pleurocerid populations referable to ebenum are much more widespread than previously thought, and that they intergrade imperceptibly with typical P. simplex populations of Tennessee drainages.  It would appear that subspecific status under simplex represents the biological situation most accurately.  See my essays of 4Feb14 and 5Mar14 from the links below for discussions about the subspecies concept as adopted here.

Populations of Pleurocera simplex ebenum often inhabit larger and softer rivers than the typical P. simplex simplex.  Their shells are heavier, paler-colored, more triangular, less likely to bear a carination in the upper whorls, and less likely to demonstrate concavity. 

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.

> Maps and Supplementary Resources

> 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.
  • I expanded upon the concept of the subspecies, as we apply that term it here in the FWGNA project, in my essays of 4Feb14, What Is a Subspecies? and 5Mar14, What Subspecies are Not.
  • In my blog post of 3Oct19, "CPP Diary: What is Pleurocera (aka Melania, aka Goniobasis, aka Elimia) ebenum," I presented evidence that Isaac Lea's 1841 nomen ebenum is best understood as a pale, heavily-shelled subspecies of P. simplex.  There are lots of excellent figures of P. ebenum in that post, both historical and recent.
  • And in my essay of 4Sept19, "CPP Diary: The Spurious Lithasia of Caney Fork," I documented a striking case of cryptic phenotypic plasticity in the P. simplex population inhabiting the Caney/Collins River system of Middle Tennessee.  The shell phenotype of that population ranged from typical in the headwaters to ebenum in the middle reaches to a form that has been mistaken for Lithasia geniculata pinguis.

> References

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 University Press, Cambridge, United Kingdom. 
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. 
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., and R.T. Dillon, Jr. 2004. Species composition and geographic distribution of Virginia’s freshwater gastropod fauna: a review using historical records. Amer Malac Bull 19:79-91. 
Turgeon, D.D. et al. 1998. Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Mollusks. Amer Fish Soc Sp Pub 26, Bethesda, Maryland..