> Habitat & Distribution

The range of Pleurocera troostiana (sl), together with all its probable variants, subspecies and synonyms, extends from the Valley-and-Ridge province of SW Virginia and East Tennessee west through the Unglaciated Interior Low Plateau of Middle Tennessee and North Alabama, north into central Kentucky.  We have records of P. troostiana (in its broadest sense) from small streams across the entire Tennessee/Cumberland drainage into the Green and Tradewater River drainages of The Ohio.

Bickel (1968) restricted the range of lyonii (as a subspecies of Goniobasis curreyana) to small streams in five Kentucky counties: Grayson, Breckinridge, Meade, Hardin, and Larue.  Our surveys found populations referable to P. troostiana lyonii significantly more widespread, extending throughout the Green River drainage of Kentucky and Tennessee, plus numerous smaller tributaries of the Ohio River in central Kentucky.  Populations of P. troostiana bearing the lyonii shell morphology are also common in tributaries of the lower Cumberland and lower Tennessee Rivers south into Alabama.

Within this region P. troostiana lyonii populations primarily inhabit 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. The FWGNA incidence rank of all four P. troostiana subspecies considered together is I-5.
  

> Ecology & Life History

Bickel (1968) offered a very complete description of the habitat of the Kentucky populations he called "Goniobasis curreyana lyoni," which he said were "commonly found on firm surfaces in riffle areas but more abundant in shallow spots near shore where water is in motion although slow moving and less turbulent."  Yes, that describes the habitat of troostiana populations exactly, throughout the entire five-state range of the species.

Bickel also focused a great deal of attention on egg masses, which he figured and described as "plano-convex, 1.3 - 2.0 mm in diameter, and partly covered with fine sand grains."  He personally observed eggs "deposited on the undersides of stones" in the month of April, but quoted an unpublished Ph.D. dissertation by W. L. Minkley to the effect that egg masses could be found "July through September, as well as during October, January, and April."

Alas, Bickel did not offer any further observations on life history.  But 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

The parent species, Pleurocera troostiana, was originally described by Isaac Lea from the vicinity of Loudon, TN (just south of Knoxville), somewhere around 1838.  All populations in East Tennessee bear shells that are variably striate, but never costate.  As FWGNA surveys expanded into Middle Tennessee, North Alabama, and Kentucky, however, we discovered populations of P. troostiana inhabiting streams bearing shells that were costate as well as striate.

The appearance of costae on the shells of P. troostiana corresponds strikingly with the distribution of Pleurocera laqueata, a costate species which ranges as far east as Walden Ridge but no further.  In my essay of 15Oct24 I presented shell-morphological evidence of troostiana/laqueata hybridization in a small tributary of the Cumberland River east of Nashville, and on 12Nov24 I generalized such findings across a wide variety of species and regions to suggest reticulate evolution in the North American Pleuroceridae.  See links below.

For the variably-striate (but uncostate) populations of East Tennessee we suggest retaining the typical nomen Pleurocera troostiana troostiana.  For populations bearing lightly costate shells we suggest P. troostiana perstriata, for those bearing heavily costate shells P. troostiana edgariana, and for the variably-shelled populations inhabiting Ohio drainages of central Kentucky P. troostiana lyonii.  A complete review of the elaborate taxonomy of Pleurocera troostiana is available as a download here [pdf].

The taxonomy of the populations we here identify as P. troostiana lyonii is a mess.  Originally described by Isaac Lea from Grayson Co, KY, the specific nomen was synonymized under Goniobasis athleta by George Tryon (1873) just eleven years later, transferred to synonymy under Goniobasis laqueata by Goodrich (1940), and then resurrected as a subspecies of Goniobasis curreyana by Bickel (1968).  But Burch, following Goodrich closely, picked up neither the specific nomen curreyana nor the subspecific nomen lyonii from Bickel, and lyonii receded into a second obscurity.  Branson (1987) did not recognize the taxon.  The nomen lyonii was resurrected a second time, as a subspecies of Pleurocera troostiana, in my 6July20 post to the FWGNA blog, available from the link below.    

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

• Dillon, R. T., Jr. (2020) The four subspecies of Pleurocera troostiana (Lea 1838), with synonymy.  FWGNA Circular 2: 1 -5. [pdf]
• Distribution of P. troostiana lyonii in drainages of The Ohio (2019)
• Distribution of P. troostiana in the Tennessee/Cumberland (2022)
• Pretty photo of living P. troostiana troostiana, courtesy of Chris Lukhaup.
  

> 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.
• In my blog post of 4Aug19, "CPP Diary: Yankees at The Gap," I documented a striking case of cryptic phenotypic plasticity in the population of P. troostiana inhabiting a little stream that runs south out of Cumberland Gap, TN.
• I used the Melania troostiana situation as an example of why Isaac Lea Drives Me Nuts in November of 2019.
• The evidence that troostiana is the oldest available name for this entire far-flung and variable species was reviewed in 6Dec19, On the Trail of Professor Troost.  And I reviewed the evidence that seven other East Tennessee nomina should be considered its junior synonyms in my post of 7Jan20, CPP Diary: The Many Faces of Professor Troost. 
• The subspecies perstriata was proposed in my essay of 15Apr20, Huntsville Hunt, and elaborated in my essay of 10May20, A House Divided.  The subspecies edgariana followed on 5June20, What is Melania edgariana?
• I proposed and justified the Kentucky subspecies P. troostiana lyonii in my essay of 6July20, The Return of Captain Lyon.  That post included a copy of Lea's original (1863) figure as well as an image of a modern topotype.
• In my essay of 15Oct24 I presented shell morphometric evidence that populations identified as P. troostiana perstriata result from Widespread hybridization between Pleurocera laqueata and P. troostiana in streams of the Tennessee/Cumberland. That essay also featured a nice map comparing the distributions of all four troostiana subspecies to that of P. laqueata.
•  And in my follow-up essay of 12Nov24 I generalized evidence of such hybridization across a variety of species and regions to suggest Reticulate evolution in the North American Pleuroceridae.
• Given the levels of hybridization documented in the essays linked above, we should not be surprised to discover that a wonderful tower of taxonomic babel has been erected to capture the rich variety of shell morphological variation associated.  See my review of [coming soon], Taxonomy Part 2, for an image of Lea's (1862) lyonii holotype. 

> 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.
Graf, D. L. (2001)  The cleansing of the Augean stables.  Walkerana 12(27): 1 - 124.
Jokinen, E.H. 1992. The Freshwater Snails (Mollusca: Gastropoda) of New York State. NY State Mus Bull 482, Albany, New York.
Lea, Isaac (1838-39) Description of New Freshwater and Land Shells.  Transactions of the American Philosophical Society (New Series) 6: 1 – 154.
Lea, Isaac (1862) Description of a new genus (Goniobasis) of the Family Melanidae and eighty-two new species. Proceedings of the Academy of Natural Science of Philadelphia 19: 262 – 272.
Scudder, N. P. (1885)  Bibliographies of American naturalists - II. The published writings of Isaac Lea, LL.D.  Bullentin of the US National Museum 23: 1 - 278.
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.
Tryon, G. W. (1873)  Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.