> Habitat & Distribution

Populations of Pleurocera potosiensis are widespread and common in rivers and streams throughout the Ozark/Ouachita highlands of Missouri, Arkansas, and eastern Oklahoma (Gordon 1980, 1982, Wu et al. 1997, Christian & Hayes 2007).  Quoting Wu and colleagues: “If a permanently flowing stream in the Ozarks contains snails, this species invariably will be present.”  We are aware of but two populations in our four-state Great Plains study area, however,  both inhabiting small tributaries of the Neosho River in the extreme southeastern corner of Kansas.  

As is typical for pleurocerid gastropods generally, populations of P. potosiensis reach maximum densities in clean, well-oxygenated lotic waters with good flow, typically on rocks, cobbles, and other firm substrates.

> 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. potosiensis 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. potosiensis, 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

Pleurocera potosiensis populations demonstrate protean levels of shell morphological variation, both within and among sample sites, especially with regard to spire height and body whorl width.  Goodrich (1939) recognized three subspecies on the basis of such variation: plebius (Anthony 1850), ozarkensis (Call 1886), and crandalli (Pilsbry 1890).  

Minton et al (2011) confirmed a significant correlation between river position and spire height in populations of P. potosiensis sampled from a stream and a spring run in central Arkansas, downstream samples tending to demonstrate shorter, broader, more robust shells.  For more about this widespread and well-documented phenomenon, which we have termed “cryptic phenotypic plasticity” (Dillon et al. 2013, Dillon 2014) see essays 23Mar11, 3June13, and 11July14 from the links below.

Minton et al. (2017) went on to explore genetic variation within and among P. potosiensis populations sampled at broad scale using 16S mtDNA sequence, and at fine scale using ISSR markers, very similar to the allozyme studies of Dillon (1984, 1988, 2020) with P. proxima.  While Minton’s fine scale ISSR analysis did show significant structuring within and between neighboring P. potosiensis populations, his larger scale 16S analysis was too weak to return any significant patterns analogous to those demonstrated by Dillon (1984).

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

• Pleurocerid distribution in The Great Plains (2024)

> 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 on P. clavaeformis, entitled Goodbye Goniobasis, Farewell Elimia.  Links are available from that essay to older resources.
• In my essay of 3June13 I documented another "Goodrichian taxon shift" in "Pleurocera acuta is Pleurocera canaliculata."  This prompted my colleagues and me to broaden the concept of Goodrichian taxon shift and rechristen it "cryptic phenotypic plasticity."
• On 11July14 I posted an essay elaborating the results of my (2014) paper on cryptic phenotypic plasticity in P. semicarinata, entitled "Elimia livescens and Lithasia obovata are Pleurocera semicarinata."  That essay also includes a couple additional figures of extreme shell morphologies.

> References

Christian, A.D. and D.M. Hayes (2007)  Diversity and distribution of freshwater gastropods from the Ozark Region of Arkansas.  Submitted to William R. Posey II, Malacologist and Commercial Fisheries Biologist, AGFC, P.O. Box 6740, Perrytown, Arkansas.  34 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. (1984) Geographic distance, environmental difference, and divergence between isolated populations. Systematic Zoology 33:69-82.  [PDF]
Dillon, R.T. Jr. (1988) The influence of minor human disturbance on biochemical variation in a population of freshwater snails. Biological Conservation 43: 137-144.  [PDF] 
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. [pdf]
Dillon, R. T. Jr. (2014)  Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata.  Zool. Stud. 53:31.  [pdf]
Dillon, R. T. Jr. (2020) Fine scale genetic variation in a population of freshwater snails. Ellipsaria 22(1): 24 - 25.  [PDF]
Dillon, R. T., S. J. Jacquemin & M. Pyron (2013) Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117-127.  [PDF]
Goodrich, C. (1939). Pleuroceridae of the Mississippi River basin exclusive of the Ohio River. Occasional Papers of the Museum of Zoology, University of Michigan, 406, 1-4.
Gordon, M.E. (1980). Recent Mollusca of Arkansas with annotations to systematics and zoogeography.  Proceedings of the Arkansas Academy of Science 34: 58-62.
Gordon, M.E. (1982). Mollusca of the White River, Arkansas and Missouri. Southwestern Naturalist, 27: 347-352.
Jones, W.C., & Branson, B.A. (1964). The radula, genital system, and external morphology in Mudalia potosiensis (Lea, 1841) (Gastropoda: Prosobranchiata: Pleuroceridae) with life history notes. Transactions of the American Microscopical Society, 83, 41-62.
Minton RL, Lewis EM, Netherland B, Hayes DM (2011) Large differences over small distances: plasticity in the shells of Elimia potosiensis (Gastropoda: Pleuroceridae). International Journal of Biology 3(1): 23–32.
Minton, R.L., B.L. McGregor, D.M. Hayes, C. Paight, and K. Inoue (2017)  Genetic structuring in the pyramid Elimia, Elimia potosiensis (Gastropoda, Pleuroceridae), with implications for pleurocerid conservation.  Zoosyst. Evol. 93(2) 437 – 449.
Wu, S-K, R.D. Oesch and M.E. Gordon (1997)  Missouri Aquatic Snails.  Missouri Department of Conservation Natural History Series No. 5, 97 pp.