> Habitat & Distribution

Our records suggest that populations of P. gabbiana range from tributaries of the Holston, Clinch and Powell Rivers in SW Virginia at least 200 km south through Tennessee to Monroe County, perhaps further.  We also have a couple records from tributaries of the Bluestone River of the Kanawha/Ohio, perhaps the result of stream capture.  Maximum population densities are reached in small, rich, hard water creeks and spring-fed streams.  FWGNA incidence rank I-4.

> 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, Pleurocera gabbiana is dioecious, eggs presumably deposited on hard substrates from spring to mid-summer.  Pleurocerid 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 no life history data are as yet available for this recently-rediscovered species, 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

Goniobasis gabbiana was described by Isaac Lea in 1862 from "Tennessee; Prof. Troost: Alabama; Prof. Tuomey" and promptly forgotten.  The nomen made subsequent reappearances in the reviews of Tryon (1873) and Graf (2001), but no additional specimens have ever been deposited in any national collection, beyond the holotype in the US National Museum.

We rediscovered P. gabbiana quite by accident, as a consequence of sampling populations of P. simplex simplex to calibrate the allozyme study of Dillon (2011).  It materialized that what we took to be a single panmictic population of P. simplex inhabiting a small stream in Maryville, TN, was in fact two reproductively isolated populations, distinguishable by the regression of their apex height on body whorl height (Dillon 2016a).   The "fat" subsample (ratio of apex height to body whorl height decreasing with age) matched the type population of P. simplex from Saltville, Virginia (Dillon & Robinson 2016).  The "skinny" subsample (ratio of apex height to body whorl height increasing with age) matched the museum type of Lea's 1862 gabbiana (Dillon 2016b).  See my posts on the FWGNA Blog of 13Sep16, 14Oct16, and 14Nov16 from the links below for more details.

> Maps and Supplementary Resources

• Pleurocera gabbiana and P. simplex in tributaries of The Ohio (2019)
• Distributions in the Tennessee/Cumberland (2022)
• Photo of P. gabbiana in the riffle of a small, marly stream.
  

> 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 described the discovery of two species of Pleurocera cryptic under P. simplex in my essay of 13Sept16, "The Cryptic Pleurocera of Maryville."  
• And see my follow-up essays, "The fat simplex of Maryville matches type" and "One Goodrich missed: the skinny simplex is Pleurocera gabbiana"  to learn how I ultimately figured out which of the two cryptic species was which.

> 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. (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. (2016a) Two reproductively isolated populations cryptic under Pleurocera simplex (Say, 1825) inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 15-16. [PDF]
Dillon, R. T., Jr. (2016b)  Match of Pleurocera gabbiana (Lea, 1862) to populations cryptic under P. simplex (Say, 1825)  Ellipsaria 18(3): 10 - 12.  [PDF]
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 (2016) The identity of the "fat simplex" population inhabiting Pistol Creek in Maryville, Tennessee.  Ellipsaria 18(2): 16-18. [PDF]
Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.
Graf, D. L. (2001)  The Cleansing of the Augean Stables, or a lexicon of the nominal species of the Pleuroceridae of recent North America, North of Mexico.  Walkerana 12: 1 - 124.
Jokinen, E.H. (1992) The freshwater snails of New York State. New York State Museum Biological Survey, New York State Museum Bulletin 482.
Smith, D.G.  (1980) Goniobasis virginica (Gastropoda: Pleuroceridae) in the Connecticut River USA. Nautilus 94:50-54.
Tryon, G. W. (1873)  Land and fresh-water shells of North America, Part IV, Strepomatidae.  Smthsonian Miscellaneous Collections 253: 1 - 435.