FWGNA > Species Accounts > Pleuroceridae > Leptoxis praerosa & "virgata"
Leptoxis praerosa praerosa (Say 1821)
Leptoxis "virgata" (Lea 1841)
  • click to view larger

> Habitat & Distribution

The range of L. praerosa was given by Goodrich (1940) as "Ohio River below Cincinnati to Elizabethtown, Illinois, together with a few tributaries; Cumberland River and branches; Duck River, Coffee County, Tennessee to mouth; Tennessee River, and lower parts of tributaries."

Our modern surveys have confirmed scattered populations of L. praerosa in the main Ohio River and some major tributaries such as the Licking, the Green, and the Wabash, as well as a few tributaries of the Cumberland – notably the Harpeth, the Stones, and way upstream in the Rockcastle River of Kentucky.  Populations of L. praerosa are much more widespread and common in the major tributaries of the Tennessee River (although not in the main Tennessee itself) from the Powell, Clinch, and Holston Rivers of southwest Virginia through the Flint, Elk, and Duck Rivers of Middle Tennessee, including Northern Alabama and a corner of North Georgia.

A population of L. praerosa seems to have been introduced into the New/Kanawha drainage, occurring sympatrically with L. carinata in Walker Creek and upper Wolf Creek in Giles and Bland Counties, Virginia.  We are also aware of a couple L. praerosa populations in western North Carolina, inhabiting tributaries of the Hiwassee (Dillon 1992).

Throughout this extensive range, L. praerosa seems to reach maximum population densities in medium-sized rivers, on rocks in riffles with good flow.  Populations are not commonly encountered in small creeks or streams, nor in larger rivers where substrates become too soft or silty.  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, L. praerosa is dioecious, eggs being deposited on hard substrates from spring to mid-summer.  Whelan and colleagues (2015) described eggs as being laid "singly in an apparently random manner" under their culture conditions.  Although we are unaware of any study specifically directed toward the life history of L. praerosa, 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

Several populations of Leptoxis praerosa from central and southern Tennessee served as controls for the allozyme surveys of Dillon & Ahlstedt (1997) and Dillon & Lydeard (1998), and for the mtDNA sequence study of Whelan & Strong (2016).  See my essay of 3Apr16 from the link below for more.  "Anculosa" is a commonly-encountered synonym for the genus.

In the original version of the web page, as published online in 2011, we referred to L. praerosa as “a widespread and well-characterized species.”  Although the former observation remains quite true, the latter not so much.

The 2013 Ph.D. dissertation of N. V. Whelan comprised six chapters, the fifth of which reported an extensive molecular phylogeny of the North American Pleuroceridae based on four genes (two mitochondrial and two nuclear) sequenced from 207 individuals sampled from 62 populations of 32 nominal species and subspecies.  His results returned evidence that populations previously identified as Leptoxis praerosa comprise two molecularly-distinct clades, apparently admixed in the Holston and Nolichucky Rivers, as though they might be reproductively isolated.  The clades do not, however, seem distinguishable by shell morphology or by any other means.  Whelan referred populations of the more-widespread (Clinch River) clade to Leptoxis praerosa, and the less-widespread (Hiwassee River) clade to Leptoxis virgata (Lea, 1841).

Isaac Lea described Anculosa virgata from a single shell collected in “Tennessee.”  Tryon considered virgata a junior synonym of subglobosa (Say 1825), which Goodrich (1940) considered a junior synonym of praerosa.  Goodrich considered A. virgata a valid species, however, more closely related to L. carinata (Brug. 1792) than to L. praerosa.

The molecular distinction documented by Whelan between the Clinch River and Hiwassee River clades, together with their sympatry in the Holston and Nolichucky, suggests to us that a pair of cryptic Leptoxis species may indeed inhabit the rivers of East Tennessee.  Thomas Say's (1821) nomen praerosa is the oldest available name for the more widespread of the pair, Isaac Lea's (1841) virgata poorly justified for the other, but nevertheless now with precedent.  Thus we have headed the present page with both nomina, and consider them both together here.

Whelan (2013) also documented some molecular divergence between the praerosa populations of East Tennessee and those inhabiting the tributaries of the Middle Tennessee, the Cumberland, and the Ohio.  He proposed to restrict Say’s nomen praerosa to the latter group and resurrect Say’s subglobosa for the former.  But given no evidence of sympatry, it seems most likely to us that the molecular divergence between these two groups is better attributable to geographic isolation.

Goodrich (1940) identified populations of openly-umbilicate Leptoxis from the Elk River, the Stones River, the Red River, and Ringgold Creek (a tributary of the Red) as Leptoxis umbilicata (Wetherby 1876).  Evans and Whelan (2014) added a possible record from the Rockcastle River in Kentucky.  Whelan (2013) was able to confirm openly-umbilicate Leptoxis in the East Fork of the Stones River, but his DNA sequence data did not return any evidence of genetic divergence between this population and nearby populations of Leptoxis praerosa.

Our surveys conducted more broadly throughout the Tennessee/Cumberland drainage system have confirmed several populations of otherwise typical Leptoxis praerosa bearing predominantly-umbilicate shells in the Stones and Red subdrainages.  The character is sporadic in populations inhabiting the upper Elk.  Intrapopulation variation such as that depicted in the figure below, together with the genetic data of Whelan (2013), suggest that L. umbilicata (Wetherby 1876) be lowered to subspecific status.

> Maps and Supplementary Resources

  • Pretty photo of living L. praerosa, courtesy of Chris Lukhaup.Click for larger image

  • Intergradation among umbilicate shell forms near Clarksville, TN.Click for larger image

> Essays

  • Although focused on the pleurocerid fauna of the Mobile Basin, the genetic survey of Whelan & Strong (2016) also included mtDNA sequence data from a North Alabama population of L. praerosa as an outgroup control.  Their results were reviewed in my essay of 3May16, Mitochondrial Superheterogeneity and Speciation.
  • I reviewed my 50 years of field and laboratory experience with pleurocerid populations of the genus Leptoxis in a blog post of 6Apr23, Growing up with Periwinkles, devoting several paragraphs to L. praerosa in particular.
  • See my essay of 9May23, Testing the Periwinkle Hypothesis, for an appreciation of N.V. Whelan's impressive (2013) DNA sequence data set drawn from 31 populations of Leptoxis sampled across eastern North America.  Among the many important results of Nathan's phylogenetic analysis was his discovery that a second, cryptic species of Leptoxis apparently co-occurrs with L. praerosa in the rivers of East Tennessee, which he identified as "L. virgata." My 9May23 essay also reprinted Nathan's pretty figure comparing the shell morphology of the two species.  

> 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. (1992)  Status survey of the knotty elimia, Goniobasis interrupta (Hald).  Report to the North Carolina Wildlife Resources Commission, Contract 92-Snai-01.  19 pp.  
Dillon, R. T. Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp.  
Dillon, R. T. Jr. & S. A. Ahlstedt (1997)  Verification of the specific status of the endangered Anthony's River Snail, Athearnia anthonyi, using allozyme electrophoresis.  Nautilus 110: 97-101.  
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., and C. Lydeard (1998)  Divergence among Mobile Basin populations of the pleurocrid snail genus, Leptoxis, estimated by allozyme electrophoresis.  Malacologia 39: 113-121.
Evans, R. & N. Whelan (2014)  Recent observation of Leptoxis from the Rockcastle River, Kentucky.  Ellipsaria 16(4): 27 - 28.
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.
Whelan, N.V. (2013)  Conservation, life history and systematics of Leptoxis Rafinesque 1819 (Gastropoda: Cerithioidea: Pleuroceridae).  Ph.D. dissertation, University of Alabama, Tuscaloosa.  157 pp.
Whelan, N. V., P.D. Johnson & P. M. Harris (2015)  Life-history traits and shell morphology in the genus Leptoxis Rafinesque, 1819.  J. Moll. Stud. 81: 85-95.
Whelan, N.V. & E. E. Strong (2016)  Morphology, molecules and taxonomy: extreme incongruence in pleurocerids (Gastropoda, Cerithiodea, Pleuroceridae). Zoologica Scripta 45: 62 – 87.