> Habitat & Distribution

The range of P. acuta (in the old sense) was mapped by Dazo (1965) as extending from Great Lakes drainages south through tributaries of the Missouri, Ohio, and Arkansas Rivers into Louisiana.  Dazo documented a range as far west as Kansas, and east into tributaries of the lower Tennessee and Cumberland Rivers, but did not recognize P. acuta extending further upstream into Alabama or East Tennessee.  Throughout that extensive range pleurocerid populations bearing shells of the acuta morphology were understood to inhabit smaller rivers and streams, not extending into the larger rivers.

Our appreciation for the biology of this phenotypically-plastic species has improved significantly in recent years, however.  We now understand that acuta is a shell variant of Pleurocera canaliculata correlated with stream size, and that populations of P. canaliculata in a broader sense do extend into the largest rivers, through Alabama and East Tennessee as far upstream as Knoxville.  The FWGNA incidence rank of P. canaliculata acuta, combined together with P. canaliculata pyrenellum and P. canaliculata canaliculata (ss), is I-5. 

> Ecology & Life History

Pleurocera canaliculata acuta is, by virtue of the excellent monograph of Dazo (1965), one of the best-known prosobranchs inhabiting North American freshwaters.  Dazo's laboratory populations plowed "somewhat sluggishly" through the sandy bottoms of their aquaria, rostrums extended, sweeping from side to side.  Gut content analysis from the field suggested a generalized grazing habit, composed of "red and green algae, desmids, and diatoms."

Both Dazo's laboratory and field observations agreed that mating takes place during the fall. The animals hibernated when water temperatures fell below 5 degrees C, emerging in the spring to lay eggs.  Dazo reported that sand-covered eggs were laid on hard surfaces in batches of varying sizes and shapes, the number of eggs per mass varying from 1 - 19.   He observed a fecundity of approximately 15 eggs/snail/day in his field population of P. canaliculata acuta, April to June.  Hatch time was approximately 2 weeks.

Two years were required to reach maturity in Dazo's lab populations, at approximately 16 mm standard shell length, "after which no appreciable growth occurred."  Both his field and his laboratory observations returned a 2:1 female bias in mature sex ratio.  Dazo suggested that adults in his Michigan populations of P. canaliculata acuta "attain an age of about three years" and "may extend to 4 years perhaps," reproducing annually.  This is life cycle Hi of Dillon (2000: 156 - 162).

The observations of Houp (1970) on a Kentucky population of P. canaliculata acuta agreed in most respects with those of Dazo in Michigan, although she recorded a field sex ratio of 1:1. Egglaying took place in July and August in Houp's study population, and her results "did not give a clear-cut indication of survivial beyond the second year." 

> Taxonomy & Systematics

See Dazo's (1965) paper for marvelously detailed anatomical drawings, notes, and observations on the muscular, digestive, reproductive, circulatory, and nervous systems of Pleurocera canaliculata acuta.  His inability to document any significant anatomical difference between Pleurocera and what was at that time called Goniobasis (or "Elimia") livescens in any respect was crucial in the subsequent unification of the two genera by Dillon (2011).  See my essay of 23March11 from the link below for more.

From its description by Rafinesque in 1831 through the nineteenth and twentieth centuries, Pleurocera acuta was recognized validly distinct at the full species level (eg, Baker 1928, Goodrich 1939).  In 2013, however, Dillon and colleagues used allele frequencies at nine polymorphic allozyme loci to show that several populations of nominal P. acuta 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 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 (Conrad 1834) and acuta (Raf 1831) as subspecies under canaliculata (Say 1821), however, by virtue of their indexing function.  See the pair of related essays I posted on the FWGNA blog in June of 2013 (links below) for a more complete discussion of the 2013 results. 

> Maps and Supplementary Resources

• Pleurocera canaliculata in drainages of The Ohio (2019)
• Pleurocerid distribution in The Great Plains (2024)

> 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

Baker, F. C. (1928) Freshwater Mollusca of Wisconsin, Part I, Gastropoda. Bull. Wisc. Geol. Natur. Hist. Survey, no. 70.  University of Wisconsin Press, Madison.
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. (1939) Pleuroceridae of the St. Lawrence River Basin. Occas. Pprs. Mus. Zool. Univ. Mich., 404, 1-4.
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.