> Biomphalaria obstructa (Morelet 1849)
    "Biomphalaria havanensis"

> Habitat & Distribution
I was most surprised when Ms. Ana Dutra-Clarke, a graduate student visiting from Brazil, showed me my first specimen of B. obstructa.   It was the summer of 1988, and she had just waded ashore from the pond at Charles Towne Landing State Park, not a mile from my home in the Charleston suburbs.  This turned out to approach the most northern record of Biomphalaria in the world, and we published the report together in 1992.

Malek (1985) gives the range of B. obstructa as Texas, Louisiana, Florida, Mexico, Puerto Rico, and Cuba, adding that “It has also been reported from California, but was probably introduced there.”  I also think it most likely that the Charleston population is the result of an artificial introduction.  The pond is largely artificial, the site heavily disturbed, and I have not subsequently collected B. obstructa elsewhere in South Carolina.  There is one lot of B. obstructa in the Georgia Museum of Natural History labeled "McIntosh County," which I have been unable to confirm.

Within the pond at Charles Towne Landing, B. obstructa is closely associated with floating vegetation.  In years when vegetation has been allowed to spread, the Biomphalaria population has expanded.  The park management has treated the pond with herbicides rather regularly in the last decade or so, and the Biomphalaria population has suffered in consequence.

> Ecology & Life history
As the host of schistosomiasis in the New World, snails of the genus Biomphalaria have been targeted for extensive research (Malek 1958, Dillon 2000: 61-66).  The Charleston population seems to display the annual, semelparous life cycle A so typical of temperate pulmonate populations.

Apparently B. obstructa is not susceptible to infection by the medically important S. mansoni (Malek 1967, Sullivan & Hu 1996), although the closely-related B. havanensis may be (Michelson 1976).  I have not observed any parasitism in the Charleston population.

> Taxonomy & Systematics
The Charleston population is specifically identical to the populations of Florida, Texas, and Louisiana (Malek, pers. comm.). Although Burch identifies this species as B. havanensis, Malek considers U.S. populations B. obstructa.

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.

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

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

>Maps of Biomphalaria distribution
Click the small map to enlarge it, or download the state-specific PDF





South Carolina (PDF)

>References
Baker, F. C. (1945) The Molluscan Family Planorbidae. Urbana: University of Illinois Press.  Baker, H. B. (1946) Index to F.C. Baker's "The Molluscan Family Planorbidae." Nautilus, 59, 127-41.  Dillon, R. T., Jr. (2000)  The Ecology of Freshwater Molluscs. Cambridge, Cambridge University Press. 509 pp.  Dillon, R. T., Jr. & A. Dutra-Clarke (1992)  Biomphalaria in South Carolina. Malacological Review, 25: 129-130.  Hubendick, B.  (1955)  Phylogeny in the Planorbidae.  Trans. Zool. Soc. London 28: 453-542.  Kuntz,R.E., Gremillion, D.H., Geckler,R.W. & Marraro,R.V. ( 1978)  Different species and geographic strains of Biomphalaria as hosts for Schistosoma mansoni (Saudi Arabia Strain).  J. Parasitol., 64: 940-941.  Malek, E. (1958)  Factors conditioning the habitat of bilharziasis intermediate hosts of the family Planorbidae. Bull. W.H.O., 18: 785-818.  Malek, E. (1967)  Susceptibility of tropicorbid snails from Louisiana to infection with Schistosoma mansoni. Am. J. Trop. Med. Hyg., 16: 715-717.  Malek, E. (1969)  Studies on "Tropicorbid" snails (Biomphalaria: Planorbidae) from the Caribbean and Gulf of Mexico areas, including the southern United States. Malacologia, 7: 183-209.  Malek, E. (1985)  Snail hosts of schistosomiasis and other snail-transmitted diseases in tropical America: A manual. Washington, D.C., Pan American Health Organization.  325 pp.  Michelson, E. (1976)  A potential intermediate host of Schistosoma mansoni from Haiti. J. Parasitol., 62: 648-649.  Sullivan, J.T. & Hu, P.C. (1996)  Fate of Schistosoma mansoni in Biomphalaria obstructa.  J. Parasitol. 82: 743-747.