> Viviparus subpurpureus (Say 1829)

> Habitat & Distribution
Clench & Fuller (1965) reported an entirely interior range for V. subpurpureus, including the Mississippi river system and several smaller Gulf drainages.  The species was not known to be invasive until the appearance of large volumes of dead shell on the shoreline of Lake Marion in 2003.  Its spectacular increase in population density may be related to a burst of macrophyte production, triggered in turn by a prolonged drought.

> Ecology & Life history
Although little specific is known about the diet and general ecology of V. subpurpureus, both grazing and filter-feeding modes have been documented in congeners.  Reproduction is apparently semelparous, some populations reaching maturity in but a single year, others requiring two years (Brown & Richardson 1992). 

> Essay
I posted an essay on invasive viviparids in South Carolina to the FWGNA web site on 29Oct03.  There are links to several additional photos.

> Taxonomy & Systematics
The taxonomy of American Viviparus has been stable since the brief monograph of Clench & Fuller (1965).  Although V. subpurpureus bears a shell broadly similar in size and form to that of the better known V. georgianus, the two are distinguishable by the rounded shoulders and color bands generally prominent on the latter.

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





South Carolina (PDF)

>References
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.  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  Richardson, T.D. & Brown, K.M. (1989)  Secondary production of two subtropical snails (Prosobranchia:Viviparidae).  J. N. Am. Benthol. Soc. 8: 229-236.