> Recommendations

Table 1 shows that 18 species of freshwater gastropods were collected at ten or fewer of the 351 snail-positive sites in South Carolina.  These species are generally introduced, undercollected, and/or inhabiting the margin of a much larger range.  Introduced species include Pomacea canaliculata, P. paludosa, Bellamya japonica, V. subpurpureus, (probably) Biomphalaria obstructa and (possibly) Viviparus georgianus.  Species approaching the southern margin of their ranges include Gyraulus parvus, Promenetus exacuous, Ferrissia rivularis, and Lymnaea humilis, and species approaching the margins of their range include Lymnaea cubensis and Hebetancylus excentricus.  Lyogyrus granum and Littoridinops tenuipes are probably undercollected by virtue of their size.

The main exception is Somatogyrus virginicus, the status of which may be cause for some conservation concern.  The seven collection sites for this species represent just four creeks in three scattered counties – Abbeville, Oconee, and Richland.  A population has also been reported to inhabit the upper Lynches River in Lancaster County.  Somatogyrus populations seem to require good water quality and a rocky substrate.  The conservation status of Somatogyrus (under several nomina) in Georgia is "G2G3" (imperiled/vulnerable), and its status in North Carolina and Virginia undetermined.  The discovery of S. virginicus in South Carolina is good news, and should prompt efforts to protect the species here and extend the search elsewhere.

There may also be cause for some conservation concern regarding Lioplax subcarinata and Gillia altilis.  Both of these fairly large and conspicuous gastropods are rare in South Carolina, but it is not clear to what extent their rarity is due to habitat degredation or to the approach of their southern range limits here.  Clench (1962) reported L. subcarinata in Atlantic drainages from New York to South Carolina, although Jokinen (1992) suggested that the species may have been extirpated in New York.  The nominal range of G. altilis is similar: Atlantic drainages from New Jersey to South Carolina (Walker 1918), although in this case Jokinen (1992) reported a true range extending further north.  In any case, a clear understanding of the conservation status of Lioplax and Gillia must await a more complete survey of North Carolina, Virginia, and the mid-Atlantic states, currently ongoing.

Table 1 also shows the freshwater gastropod species that might have been predicted to occur in South Carolina on the basis of Mazyck’s (1913) survey of historic records and the NatureServe Explorer database, version 2/2005.  The differences in the three lists are striking in some respects, and may reflect the general neglect the state has suffered since twentieth-century improvements in transportation made regional surveys of freshwater biota practical.  A total of 14 names on the Mazyck list have been subsumed into synonymy, as well as 4 names on the NatureServe list.

Misidentification almost certainly accounts for three of Mazyck’s Goniobasis (vanuxemii, acutocarinata, and carinifera) as well as Lymnaea palustris, Physa gyrina, and Ferrissia parallela.  I am less sure about the little planorbid, Gyraulus deflectus.  It's occurrence in South Carolina is at least plausible, and additional sampling efforts may well turn them up.

The Pomatiopsis “hinkleyi” listed on the NatureServe database is a junior synonym of P. lapidaria according to Hubricht (1960), who collected it near the Little Salkehatchie River north of Ehrhardt, Bamberg Co.  We have been unable to confirm the presence of Pomatiopsis in the vicinity of Ehrhardt or anywhere else in South Carolina, but have no reason to doubt Hubricht’s record.  Pomatiopsis lapidaria is an amphibious species widely distributed through eastern interior drainages.  Its occurrence in South Carolina, or indeed in any southern Atlantic drainage, would be extralimital.

So in summary, SC does not appear to host any endangered freshwater gastropods at present.  Its waters drain environments not strikingly different from those of states bordering on the north and south.  Its 29 species include a set of statewide occurrence, a subset whose distribution reflects artificial introduction or undercollection, and a set whose regional distribution seems constrained by climate and topography.  Several species of the piedmont and upper coastal plain, especially those requiring rocky substrate, seem to have been adversely impacted by agriculture and subsequent erosion.  Somatogyrus virginicus, newly reported for this state, will bear further attention in this regard.  Two other species (Lioplax subcarinata and Gillia altilis) are rare in South Carolina and may present cause for conservation concern, depending on their status in the more central portions of their range.

>References

Burch, J., and J. Tottenham.  1980.  North American freshwater snails: species list, ranges, and illustrations. Walkerana 3: 1-215.  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: 261-287.  Hubendick, B.  1951.  Recent Lymnaeidae.  Their variation, morphology, taxonomy, nomenclature, and distribution. Kungl. Svenska Vetensk. Akad. Handl. 3: 1-223.  Hubricht, L.  1960.  Pomatiopsis lapidaria on the southern Atlantic coastal plain, with remarks on the status of P. praelonga and P. hinkleyi. Nautilus 74: 33-34.  Jokinen, E.  1992.  The freshwater snails (Mollusca: Gastropoda) of New York State. New York State Museum Bulletin 482: 1-112.  Mazyck, W.  1913.  Catalog of Mollusca of South Carolina, P. Rea (eds.). Contributions from the Charleston Museum, vol. II. Charleston, SC, Charleston Museum.  Walker, B.  1918.  A Synopsis of the Classification of the Freshwater Mollusca of North America, North of Mexico. Misc. Pubs., vol. 6. Ann Arbor, University of Michigan Press.  Watson, C.  2000.  Results of a survey for selected species of Hydrobiidae (Gastropoda) in Georgia and Florida. Pp 233 - 244 In Freshwater Mollusk Symposia Proceedings, Tankersley, Wamolts, Watters, Armitage, Johnson, & Butler (eds.). Columbus, Ohio Biological Survey.