> Habitat & Distribution

Goodrich (1940) gave the range of P. pyrenellum as "tributaries of the Tennessee River in Morgan and Limestone counties, Alabama, and Walker County, Georgia."  In the original release of this species page (8/11), we reported scattered populations in Tennessee tributaries much further north, extending almost to Knoxville, as well as in the Sequatchie River and its tributaries. Subsequently we have identified Pleurocera populations bearing the pyrenellum shell morphology in Tennessee River tributaries throughout North Alabama, with scattered records in the drainages of the Duck River and Red/Cumberland in Middle Tennessee. Populations seem to reach maximum densities in small to moderate-sized rivers, in regions of good flow.

Our understanding of the biology of these populations was augmented significantly, however, by the discovery of Dillon et al. (2013) that Conrad's "P. pyrenellum" is conspecific with populations referred to as "Pleurocera canaliculata" in the larger rivers, and "Pleurocera acuta" elsewhere throughout the greater Midwest (more below).  The range of P. canaliculata (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

Populations of P. canaliculata inhabiting smaller streams often 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 Tennessee and P. acuta further north.  But in 2005, Campbell & Harris reported negligible CO1 sequence divergence between three P. canaliculata sampled from the main Tennessee River in North Alabama (one misidentified as “P. alveare”) and an individual P. pyrenellum sampled from nearby Limestone Creek.  And 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 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 my essays of June and July (from the links below) for more.

Goodrich’s (1940) “Group of Pleurocera pyrenellum” included brumbyi, currierianum, viridulum, and trochiformis.  Our field work in North Alabama suggests that the first three of these nomina, and P. striatum as well, are junior synonyms of pyrenellum (see footnote to my essay of 10May20, link below).  Our observations further suggest that viridulum (from Chickamauga Creek, Walker County, GA) may be a synonym of P. clavaeformis.
 

> Maps and Supplementary Resources

• Distribution of P. canaliculata in the Tennessee/Cumberland (2022)

> 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.
• 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.
• See footnote [10] in my essay of 10May20, A House Divided, for observations on Pleurocera brumbyi (Lea 1852), striatum (Lea 1862), and currieranum (Lea 1863).  

> References

Campbell, D. and P. Harris (2005)  Report on molecular systematics of poorly-known freshwater mollusks of Alabama.  Alabama Department of Conservation and Natural Resources, State Wildlife Grant Project Report.  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. (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.