FWGNA > Species Accounts > Viviparidae > Campeloma decisum crassulum
Campeloma decisum crassulum (Raf. 1819)
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> Habitat & Distribution

Combined with all its probable synonyms, Campeloma decisum (ss) ranges throughout eastern North America, well up into Canada and down to Florida (Clarke 1981, Thompson 1999). Populations seem to reach maximum abundance burrowing in sandy bottoms where the current is sufficient to oxygenate the water column, especially in the larger rivers of the Interior Plains, the upper Atlantic Coastal Plain, and the Piedmont.

Populations bearing the markedly-robust crassulum shell morphology are not common, however.  We have a few records from tributaries of the Kentucky and Licking Rivers, as well as the main Ohio itself.  The FWGNA incidence rank for both C. decisum crassulum and C. decisum (ss) considered together I-5.

> Ecology & Life History

Little is known regarding the diet of Campeloma.  The burrowing habit and peculiar radular morphology displayed by these snails imply an ability to filter feed, as has been documented for Viviparus.  But the snails have almost certainly retained the ability to graze or harvest deposits on soft sediments as well. There are reports that Campeloma can be baited with carrion.

Parthenogenesis has evolved three times in the freshwater Gastropoda, all three occasions (Campeloma, Potamopyrgus, and the thiarids) in ovoviviparous brooders (Dillon 2000:109). Some populations of Campeloma appear comprised entirely of parthenogenic females, others appear to reproduce entirely by outcrossing, and some populations display a mixture of the two modes (Johnson & Bragg 1999, Johnson & Leefe 1999, Johnson 2000, Crummett & Wayne 2009). 

Only a single year is required for maturation in some populations, two in others, and both semelparous and iteroparous reproduction have been reported (Vail 1978, Brown et al. 1989, Brown & Richardson 1992).  Jokinen’s (1983) analysis of the distribution of C. decisum in Connecticut and New York led her to classify it as an “A-B tramp,” typically present only in the more species-rich communities.  Dillon’s (2000: 360 - 363) USR reanalysis of these data suggested that C. decisum populations in Connecticut seem to be Undifferentiated with respect to life history adaptation.

> Taxonomy & Systematics

Clench (1962) reviewed all 49 specific nomina historically assigned to the genus Campeloma, reducing their number to 14 by synonymy.  Burch (1989) further reduced the number of species to 8, among which was C. crassulum, which he distinguished by its "large, heavy and ponderous" shell. 

The widespread occurrence of parthenogenesis in this group voids the biological species concept and necessitates a retreat to the morphological.  So since we ourselves have generally been unable to distinguish Campeloma populations anywhere in the eastern United States, by shell or any other morphological criterion, we here refer all to the oldest available name, C. decisum (Say, 1816).

The crassulum morphology is an exeption.  Our field observations suggest to us that some populations of C. decisum tend to develop especially heavy and ponderous shells in the same large-river situations where such a morphology is developed by pleurocerid populations, possibly in response to increased predation by shell cracking.  They appear to demonstrate a viviparid example of cryptic phenotypic plasticity, originally described for pleurocerids by Dillon and colleagues (2013) and Dillon (2014).  So by analogy with the pleurocerid situation, we have preserved Rafinesque's (1819) nomen crassulum as a subspecies of Say's decisum.  See the essays from the links below for more about cryptic phenotypic plasticity and its taxonomic treatment here.

> Supplementary Resources

> Essays

> References

Burch, J. B. (1989)  North American Freshwater Snails.  Malacological Publications, Hamburg, Michigan.  365 pp.
Brown, K.M. & Richardson, T. D. (1992) Phenotypic plasticity in the life histories and production of two warm-temperature viviparid prosobranchs. Veliger 35: 1-11.
Brown, K. M., Varza, D.& Richardson, T. D. (1989) Life histories and population dynamics of two subtropical snails (Prosobranchia:Viviparidae). J. N. Am. Benthol. Soc. 8: 222-228.
Chamberlain, N. A. (1958)
 Life history studies of Campeloma decisum.  The Nautilus 72: 22 - 29.
Clench, W. (1962)
A catalogue of the Viviparidae of North America with notes on the distribution of Viviparus georgianus, Lea. Occas. Pprs. on Mollusks, Mus. Comp. Zool. Harvard, 2, 261-87.
Clench, W. & Fuller, S. (1965)
The genus Viviparus in North America. Occas. Pprs. on Mollusks, Mus. Comp. Zool. Harvard, 2, 385-412.
Crummett, L. T. & M. L. Wayne (2009)
Comparing fecundity in parthenogenetic versus sexual populatons of the freshwater snail Campeloma limum: is there a two-fold cost of sex? Invert. Biol. 128: 1 - 8.
Dillon, R. T., Jr. (2000)
 The Ecology of Freshwater Molluscs.  Cambridge University Press, Cambridge, England. 509 pp.
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., S. J. Jacquemin & M. Pyron (2013) 
Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata.  Hydrobiologia 709: 117 – 127.  [html]  [pdf]
Harvey, M., Vincent, B., & Vaillancourt, G. (1983)
(Development and fecundity of Campeloma decisum (Say) (Gastropoda: Prosobranchia) in a cold climate.) Naturaliste Canadien 110: 335-342.
Imlay, M. J., Arthur, J.W., Halligan, B.J., & Steinmetz, J.H. (1981) Life Cycle of the Freshwater Snail Campeloma decisum (Viviparidae) in the Laboratory. Nautilus 95: 84-88.
Johnson, S. G. (1992) Spontaneous and hybrid origins of parthenogenesis in Campeloma decisum (freshwater prosobranch snail). Heredity 68: 253-261.
Johnson, S. G. (2006)  Geographic ranges, populaton structure, and aes of sexual and parthenogenetic snail lineages.  Evolution 60: 1417-1426.
Johnson, S. G. & Bragg, E (1999) Clonal diversity and polyphyletic origins of hybrid and spontaneous parthenogenetic Campeloma (Gastropoda: Viviparidae) from the southeastern United States. Evolution 53: 1769-1781.
Johnson, S. G. & Leefe, W. R. (1999) Evolution and ecological correlates of uniparental reproduction in freshwater snails. J. Evol. Biol. 12: 1056-1068.
Johnson, S. G., Lively, C. M. & Schrag, S. J. (1995) Age and polyphyletic origins of hybrid and spontaneous parthenogenetic Campeloma (Gastropoda: Viviparidae) from the southeastern United States. Experientia (Basel) 51: 498-509.
Johnson, S. G., & Howard, R. S. (2007)  Constrasting patterns of synonymous and nonsynonymous sequence evolution in asexual and sexual frshwater snail lineages.  Evolution 61: 2728-2735.
Jokinen, E. (1983) The freshwater snails of Connecticut.  State Department of Environmental Protection Bulletin 109, 83 pp.
Jokinen, E. (1987) Structure of freshwater snail communities: Species-area relationships and incidence categories.  Amer. Malac. Bull. 5: 9 - 19.
Karlin, A.A., Vail, V.A. & Heard, W.H. (1980) Parthenogenesis and biochemical variation in southeastern Campeloma geniculum (Gastropoda: Viviparidae). Malacol. Rev., 13: 7-15.
Richardson, T.D. & Brown, K.M. (1989) Secondary production of two subtropical snails (Prosobranchia:Viviparidae). J. N. Am. Benthol. Soc. 8: 229-236.
Selander, R.K., E.D. Parker & R.A. Browne (1977)  Clonal variation in the parthenogenetic snail Campeloma decisa (Viviparidae)  Veliger 20: 349-351.
Vail, V.A. (1977) Comparative reproductive anatomy of 3 viviparid gastropods. Malacologia 16: 519-520.
Vail, V.A. (1978) Seasonal reproductive patterns in 3 viviparid gastropods. Malacologia 17: 73-97.