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 other
species subsequently reported (Johnson et al. 2013), giving
synonyms commonly encountered in the modern literature.
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/viator, and Hebetancylus
excentricus. Three species more common to the
north also seem to reach their southern limits – Leptoxis carinata, Physa gyrina, and Planorbula armigera.
Setting aside species reaching their (otherwise broad) range limits, as
well as the invasive species Cipangopaludina
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.