FWGNA > Freshwater Gastropods of North Carolina > Discussion
Discussion
North Carolina Atlantic Drainages

The 36 gastropod species confirmed from North Carolina Atlantic drainages are listed in Table 1, ranked by their number of records in our database. (Note that the two subspecies of P. catenaria were combined for this analysis.)  This list is compared to the checklist of Dawley (1965) and the spurious review of Johnson and colleagues (2013), giving synonyms as necessary.

As seems to be the case throughout the southeastern United States generally, few North Carolina freshwater gastropod species are associated with particular rivers or drainages. The distributions of several species seem, on the other hand, to broadly correlate with US EPA ecoregions. Pleurocera proxima is characteristic of the Blue Ridge and Piedmont ecoregions. Pleurocera catenaria, P. virginica, and Somatogyrus virginicus were collected from the Piedmont ecoregion east into the southeastern plains. The Southeastern Plains and Middle Atlantic Coastal Plain Ecoregions hosted Helisoma trivolvis, Gyraulus parvus, and Physa carolinae.  Apparently restricted to the Coastal Plain were Physa pomilia and Promenetus exacuous.

North Carolina also apparently encompasses sufficient latitude that the distributions of several of its freshwater gastropod species seem to reflect a north – south gradient. Three species more common to the south seem to reach or approach their northern limits in the state – Viviparus intertextus, Lymnaea cubensis, and Hebetancylus excentricus.  Three species more common to the north also seem to reach their southern limits – Leptoxis carinata, Physa gyrinaand Planorbula armigera.

Setting aside species reaching their (otherwise broad) range limits, as well as the invasive species Bellamya japonica, Viviparus georgianus and Melanoides tuberculata, Table 1 shows that three species were represented in our database by fewer than 10 records: Helisoma magnificum, Helisoma eucosmium, and the Waccamaw Floridobia. All three of these are endemic to North Carolina as far as is known, and their rarity would appear to be genuine, as may be judged by their FWGNA incidence ranks I-2.

Table 1 also shows entries for seven species of freshwater gastropods that might have been expected to inhabit the Atlantic drainages of North Carolina, but which our surveys have not confirmed.  Most of these are reaching the southern (or eastern) margins of much larger ranges in North Carolina (if not exceeding them!) and are expected to display very spotty distributions: Fontigens nickliniana, Probythinella emarginata, Valvata sincera, and Gyraulus deflectus.  Helisoma ("Planorbella") duryi would be reaching the northern margin of its range in North Carolina, displaying a spotty distribution for the same reason.

One of the species listed at the bottom of Table 1 is invasive, Pomacea paludosa, and may indeed soon arrive in the Tarheel State.  The remaining entry, Pomatiopsis lapidaria, is so amphibious as to be most commonly sampled by landsnail researchers, and was certainly undercollected by the survey methods employed here.

> References

 
Dawley, C. (1965)  Checklist of freshwater mollusks of North Carolina.  Sterkiana 19: 35-39.  
Johnson, Bogan, Brown, Burkhead, Cordeiro, Garner, Hartfield, Lepitzki, Mackie, Pip, Tarpley, Tiemann, Whelan & Strong (2013)  Conservation status of freshwater gastropods of Canada and the United States.  Fisheries 38: 247- 282.