> Discussion
   Virginia Atlantic Drainages

The 34 gastropod species and subspecies inhabiting Virginia Atlantic drainages are listed in Table 1, ranked by their number of records in our database. This list is compared to the result of a query to the NatureServe Explorer database performed on 1/2007, as well as to the historical review of Stewart & Dillon (2006).

As would seem to be the general situation throughout the southern Atlantic drainages, none of the freshwater gastropod species listed in Table 1 is obviously associated with or limited to a particular river drainage.  Rather, our survey suggests a set of species that range throughout the state and a set whose distributions seem broadly correlated to ecoregion or physiographic province.

Species ranging broadly throughout the state include the cosmopolitan Physa acuta, Menetus dilatatus, Lymnaea columella, and Ferrissia rivularis as well as the more patchily-distributed Campeloma decisum and Laevapex fuscus.

The fauna of the coastal plain includes Littoridinops tenuipes, Physa pomilia, Physa species A, Helisoma trivolvis, Promenetus exacuous and (generally) Amnicola and Lyogyrus.  Characteristic of the Piedmont ecoregion are Somatogyrus virginicus, Goniobasis virginica, G. catenaria, G. proxima, Leptoxis carinata, Helisoma anceps, and Lymnaea humilis, the last five of which range westward.  Fontigens orolibas appears to be narrowly endemic to the Blue Ridge ecoregion.  The other three Fontigens species (nickliniana, morrisoni, and bottimeri) appear restricted to the Ridge and Valley portion of our study area, as do Goniobasis semicarinata and Physa gyrina.

The confirmed freshwater gastropod fauna of Virginia Atlantic drainages as listed in Table 1 corresponds fairly well to the on-line database of NatureServe as well as to the historical list of Stewart & Dillon.  Setting aside those elements of the fauna known only from the Tennessee and Ohio drainages, and combining synonyms as necessary, our 34 species matched 31 in the former list and 30 in the latter.  Neither NatureServe nor Stewart & Dillon listed Physa species A (as yet to be described), Hebetancylus excentricus (very spottily distributed), or Bellamya japonica (likely confused with B. chinensis).  The Stewart & Dillon list subsumed Goniobasis catenaria dislocata under G. catenaria s.s., and missed Physa pomilia, whose taxonomic status was only recently elucidated by Dillon et al. (2007).  The NatureServe list missed Goniobasis semicarinata, whose range into Virginia Atlantic drainages has been poorly documented until the present survey.

Both the NatureServe list and the survey of Stewart & Dillon did include, however, ten freshwater gastropod species which might range into Virginia Atlantic drainages but which were not confirmed in the present survey.  These will be the focus of our section on conservation recommendations following.