> Habitat & Distribution

The range of P. canaliculata (in the old, narrow-sense) was given by Goodrich (1940) as extending from the Ohio River in the vicinity of Pittsburgh through Illinois, south through Kentucky into the Tennessee drainage.  Throughout that extensive range, robustly-shelled populations of P. canaliculata are restricted to larger rivers.  Our surveys have confirmed large populations referable to P. canaliculata canaliculata throughout the main Ohio River and most of its major tributaries (e.g. Wabash, Green, Kentucky, Licking, Kanawha), the main Tennessee River upstream to the vicinity of Chattanooga plus major tributaries (e.g. Duck, Elk, Flint, Clinch), and in many major tributaries of the Cumberland (e.g. Caney, Stones, Harpeth, Red).  Populations of P. canaliculata do not seem as dependent on solid substrates as most other pleurocerids, often being found on firm soft bottoms as well as on rip-rap stones.

Our understanding of the biology of this species has been augmented significantly, however, by the discovery of Dillon et al (2013) that lightly-shelled populations previously identified as P. pyrenellum in Tennessee drainages and P. acuta throughout the greater Midwest are conspecific with P. canaliculata (more below).  The range of the species (in its broader, more modern sense) is now understood to include the Great Lakes as well as Mississippi drainages, and to extend as far north as Minnesota, southern Ontario, New York and Vermont. Considering all subspecies together, the FWGNA incidence rank of Pleurocera canaliculata is I-5.

> Ecology & Life History

Pleurocerids are generalized grazers, and where present in high densities can have a significant effect on energy flow (Dillon 2000: 86 - 91, see also Dillon & Davis 1991).

Like other pleurocerids, P. canaliculata 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).  See Whelan & Strong (2014) for observations on the seasonal reproductive anatomy of the female.  The life history observations of Magruder (1934) for a typical, large-river population and those of Dazo (1965) and Houp (1970) for small-stream populations of the “acuta” form agree that two years are required for maturity, and that several years of iteroparous reproduction can be expected thereafter, as is the case for pleurocerids generally.  This is life cycle Hi of Dillon (2000: 156 - 162). 

> Taxonomy & Systematics

Variation in the grooves, spiral cords, nodules, general robustness, and other aspects of shell morphology in P. canaliculata populations led nineteenth-century authors to propose a luxuriant profusion of names for this single widespread species (Goodrich 1934, 1937, 1941).  Goodrich’s (1940) “Group of Pleurocera canaliculata” included three other species he regarded as valid (nobile, parvum, and postelli) as well as five subspecies for canaliculata and 44 junior synonyms.  We are unable to distinguish P. nobile from P. canaliculata, nor distinguish P. parvum or P. postelli  (Lea 1862) from P. clavaeformis unciale.

Populations of P. canaliculata inhabiting smaller streams tend to mount shells qualitatively lighter and more slender than the typical shells borne by populations of the large rivers.  For almost 200 years, such lightly-shelled populations were identified as P. pyrenellum in tributaries of the Tennessee and P. acuta further north.  But in 2013, Dillon and colleagues used allele frequencies at nine polymorphic allozyme loci to show that several populations of nominal P. acuta and P. pyrenellum were each more genetically similar to the P. canaliculata population immediately downstream than any of these populations was to any nominal conspecific.  We then used landmark-based morphometics to explore one historically important acuta-to-canaliculata transition in greater detail, that of the Wabash River in Indiana.

It seems likely to us that the difference in shell robustness that led taxonomists to distinguish acuta and pyrenellum from canaliculata for almost 200 years may be ecophenotypic responses to differing predation pressures in big rivers and small streams. This phenomenon was dubbed "cryptic phenotypic plasticity" by Dillon and colleagues (2013).  We have suggested the retention of the nomina pyrenellum and acuta as subspecies, however, by virtue of their indexing function.  See the pair of essays I posted on the FWGNA blog in June of 2013 (links below) for more. 

> Maps and Supplementary Resources

• Distribution of P. canaliculata in drainages of The Ohio (2019)
• Distribution of P. canaliculata in the Tennessee/Cumberland (2022)
• Pretty photo of living Pleurocera canaliculata, courtesy of Chris Lukhaup.
  

> Essays

• Pleurocera canaliculata made a small (but important) guest appearance in my blog post of 10Nov10, Joe Morrison and the great Pleurocera controversy.
• 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 offered a (rather formal) review of the paper by Dillon, Jacquemin & Pyron in my essay of 3June13, Pleurocera acuta is Pleurocera canaliculata.
• On 18June13 I posted a much more personal account of the observations (and wanderings, and blunderings) that ultimately culminated in the research of Dillon, Jacquemin & Pyron, Pleurocera canaliculata and the process of scientific discovery.
• The biological and taxonomic relationships between P. canaliculata canaliculata and P. canaliculata pyrenellum were touched upon briefly in a pair of related essays, What Is A Subspecies? (4Feb14) and What Subspecies Are Not (5Mar14).
• I reviewed the entire phenomenon of cryptic phenotypic plasticity in P. canaliculata in my blog post of 2June16, The Shape-shifting Pleurocera of North Alabama.  That essay featured several good figures illustrating the range of shell morphology that can be displayed by populations of this 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. (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., S. J. Jacquemin & M. Pyron (2013)  Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117 – 127.  [html]  [pdf]
Goodrich, C. (1934)  Studies of the gastropod family Pleuroceridae II.  Occas. Pprs. Mus. Zool. Univ. Mich., 295: 1 - 6.
Goodrich, C. (1937)  Studies of the gastropod family Pleuroceridae VI.  Occas. Pprs. Mus. Zool. Univ. Mich., 347: 1-12.
Goodrich, C. (1940) The Pleuroceridae of the Ohio River drainage system.  Occas. Pprs. Mus. Zool. Univ. Mich., 417: 1-21.
Goodrich, C. (1941)  Studies of the gastropod family Pleuroceridae VIII.  Occas. Pprs. Mus. Zool. Univ. Mich., 447: 1-13.
Houp, K. (1970)  Population dynamics of Pleurocera acuta in a central Kentucky limestone stream.  Amer. Midl. Natur. 83: 81-88.
Jokinen, E.H. (1992) The freshwater snails of New York State. New York State Museum Biological Survey, New York State Museum Bulletin 482.
Magruder, S. R. (1934)  Notes on the life history of Pleurocera canaliculata undulatum Say.  The Nautilus 48: 26-28.
Smith, D.G.  (1980) Goniobasis virginica (Gastropoda: Pleuroceridae) in the Connecticut River USA. Nautilus 94:50-54.
Strong, E. E.  (2005)  A morphological reanalysis of Pleurocera acuta Rafinesque 1831 and Elimia livescens (Menke 1830).  The Nautilus 119: 119-132.
Whelan, N.V. & E. E. Strong (2014)  Seasonal reproductive anatomy and sperm storage in pleurocerid gastropods (Cerithioidea: Pleuroceridae)  Can. J. Zool. 92:989-995.