> Physa pomilia Conrad 1834
    "Physella heterostropha pomilia"

> Habitat & distribution
This species was incorrectly synonymized under P. heterostropha by George Te (in Burch). Te did recognize the pomilia subspecies hendersoni as distinct, however, and suggested a large range – throughout the southeastern United States up to West Virginia, Tennessee, and Missouri. It seems more likely that the range of true P. pomilia is more restricted. In southern Atlantic drainages it is presently confirmed only from scattered slow-moving rivers in the coastal plain. The species certainly extends through the southeast as far as Alabama, but confusion with P. acuta is very likely. It is typically found on emergent vegetation and debris in quiet backwaters.

> Ecology & Life History
Our laboratory cultures of P. pomilia reach maturity only 5 – 6 weeks post hatch, and shell length of only 5 – 6 mm. This is about two weeks earlier and 1 – 2 mm smaller than typical P. acuta raised under similar conditions.

> Taxonomy & Systematics
Although outwardly quite similar to P. acuta, sequence data and penial morphology both confirm that P. pomilia is distinct (Wethington 2004a, Wethington & Lydeard 2007). Our laboratory mating experiments (Dillon et al. 2007) have returned evidence of both premating and postmating reproductive isolation between acuta and pomilia as well.

The taxonomic history of P. pomilia is a long and checkered one. Conrad originally described P. pomilia from Randons Creek near Claiborne, Alabama. Clench (1925) described a subspecies, P. pomilia hendersoni, from Yemassee, Beaufort County, South Carolina. George Te (1978) synonymized pomilia under heterostropha and raised hendersoni to the rank of full species. It was this Te classification of the Physidae that was adopted by Burch in his influential (1980, 1982) monograph of the North American freshwater snails.

Dillon et al. (2002) showed, however, that P. heterostropha is a synonym of the cosmopolitan P. acuta. So in the previous (3/04) version of this web site, I recognized three physids in South Carolina: P. acuta, P. hendersoni, and the undescribed species A.  But Dillon, Robinson & Wethington (2007)  have recently completed a series of mate choice tests and no-choice breeding studies confirming Clench’s (1925) impression that hendersoni populations from Yemassee are not reproductively isolated from P. pomilia collected at its Alabama type locality. Our South Carolina populations are at best subspecies of P. pomilia.

For notes regarding the placement of pomilia in the genus Physa, rather than Physella, see my essay of 12Oct07 below.

> Essay 
The phylogenetic analysis of Wethington & Lydeard (2007) prompted me to review the systematics of the Physidae on 12Oct07.

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



North Carolina (PDF)

South Carolina (PDF)

Georgia (PDF)

> References
Burch, J., and J. Tottenham (1980) North American freshwater snails: species list, ranges, and illustrations. Walkerana 3: 1-215. Burch, J. B. (1982) North American freshwater snails: Identification keys, generic synonymy, supplemental notes, glossary, references, index. Walkerana 4: 216 - 365. Clench, W. J. (1925) Notes on the genus Physa with descriptions of three new subspecies. Occas. Pprs. Mus. Zool. Univ. Mich. 161: 1 – 10.   Dillon, R. T., J. D. Robinson, and A. R. Wethington (2007)  Empirical estimates of reproductive isolation between the freshwater pulmonates Physa acuta, P. pomilia, and P. hendersoni.  Malacologia 49: 283-292.  Dillon, R. T., Jr., A. R. Wethington, J. M. Rhett, and T. P. Smith (2002) Populations of the European freshwater pulmonate Physa acuta are not reproductively isolated from American Physa heterostropha or Physa integra. Invert. Biol. 121(3):226-234. Te, G. (1979) New classification system for the family Physidae. Arch. Moll., 110, 179-84. Te, G. A. (1978) The systematics of the family Physidae (Basommatophora: Pulmonata). Ph. D. Dissertation, University of Michigan. 325 pp. Wethington, A. R. (2004a) Phylogeny, taxonomy, and evolution of reproductive isolation in Physa (Pulmonata: Physidae) Ph.D. dissertation, University of Alabama, Tuscaloosa. Wethington, A. R. (2004b) Family Physidae. A supplement to the workbook accompanying the FMCS Freshwater Identification Workshop, University of Alabama, Tuscaloosa. 24 pp. (PDF) Wethington, A.R., R. T. Dillon, & J. M. Rhett. (in prep.) Allozyme, 16s, and CO1 sequence divergence among populations of the cosmopolitan freshwater snail, Physa acuta.  Wethington, A. R. & C. Lydeard (2007)  A molecular phylogeny of Physidae (Gastropoda: Basommatophora) based on mitochondrial DNA sequences.  J. Molluscan Stud. 73: 241 - 257.