> Gyraulus deflectus (Say 1824)

> Habitat & Distribution
Gyraulus deflectus reaches the southern edge of its geographic range in Virginia, occurring much more commonly throughout mainland Canada north to the central Arctic, and south to Ohio, Illinois, Nebraska, and Idaho (Clarke 1981, Burch 1989, Jokinen 1992).  The literature contains one record of a North Carolina population we have been unable to confirm (Flowers & Grover 1993).  Throughout its range, G. deflectus populations inhabit quiet mesotrophic and eutrophic bodies of water, including wetlands, and shores of rivers, ponds, and lakes (Baker 1928, Clarke 1979, Jokinen 1992, Stewart and Dillon 2004).  It has been reported from mud, sand, living vegetation, decomposing organic matter, and logs at depths of 0.3-9 m (Baker 1928, Harman 1972, Clarke 1981, Pip 1985, Jokinen 1992).  In a survey of gastropods inhabiting the Precambrian Shield, Manitoba, Pip (1985) found Gyraulus deflectus in 56% of lakes greater than 10 ha in size, and 44% of rivers greater than 2 m deep, but never found it in ponds less than 10 ha and creeks less than 2 m deep.  At New York and Connecticut sites harboring this species, pH ranged from 5.6-8.5, and calcium concentrations ranged from 1-89 ppm (Jokinen 1992).


> Ecology & Life history
Jokinen (1987) classified G. deflectusas a “High-S species”, characterized by low dispersal rates, good competitive ability, a tolerance for low resource (i.e., food) levels, and persistence at low population densities.  Egg capsules are small, gelatinous and often contain 2-5 eggs (Clarke 1981).  A Connecticut population had a bivoltine life cycle, with eggs first appearing when water temperature exceeded 23 C in late June or July (Jokinen 1985, 1992).  Hatchlings from that brood matured and produced a second batch of eggs from early September through early October, and these autumn-hatched young overwintered and produced eggs the following spring - life cycle type B(is) of Dillon (2000).   Analysis of Jokinen's data on the distribution of freshwater gastropods in Connecticut led Dillon (2000: 360-364) to classify G. deflectus as Undifferentiated with regard to life history traits.

> Taxonomy & Systematics
The classification of the Planorbidae proposed by the tag team of Baker (1945) and Hubendick (1955) remains, after 50 years, the basis for our understanding of this large and diverse family of pulmonates worldwide.   See Essay #1 below.

The assignment of deflectus to the worldwide genus Gyraulus has remained stable.  Gyraulus hirsutus (Gould) is a synonym. 

Essay #1
The Classification of the Planorbidae.  1 Figure.

> Hubendick (1955)
classification of the Planorbidae, applied to North America.

 
>References
Baker, F.C. (1928) The Fresh Water Mollusca of Wisconsin: Part I. Gastropoda.  Wisconsin Academy of Sciences, Arts, and Letters.  Madison, Wisconsin.  Baker, F. C. (1945) The Molluscan Family Planorbidae. Urbana: University of Illinois Press.  Burch, J.B. (1989) North American Freshwater Snails. Malacological Publications, Hamburg, Michigan, USA.  Clarke, A.H. (1979) Gastropods as indicators of lake trophic stages. Nautilus 93:138-142.  Clarke, A.H. (1981) The Freshwater Mollusks of Canada. National Museums of Canada, Ottawa, Ontario, Canada.  Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press.  509 pp.  Flowers, J., & C. Grover (1993) New molluscan (Gastropoda and Bivalvia) records for the Neuse River basin, North Carolina. Brimleyana 19: 61-64.   Harman, W.N. (1972) Benthic substrates: their effect on fresh-water Mollusca. Ecology 53:271-277.  Hubendick, B.  (1955)  Phylogeny in the Planorbidae.  Trans. Zool. Soc. London 28: 453-542.    Jokinen, E. H. (1985) Comparative life history patterns within a littoral zone snail community.  Verh. Internat. Verein. Limnol. 22: 3292-99.   Jokinen, E.H. (1987) Structure of freshwater snail communities: species-area relationships and incidence categories. American Malacological Bulletin 5:9-19.  Jokinen, E.H. (1992) The freshwater snails of New York State. New York State Museum Biological Survey, New York State Museum Bulletin 482.   Pip, E. (1985) The ecology of freshwater gastropods on the southwestern edge of the Precambrian Shield. Canadian Field Naturalist 99:76-85.  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.