Invertebrate Cave Fauna 
129 
eyed, pigmented spring populations; the former probably evolved directly 
from the latter. Spring populations of the Fontigens orolibas “complex” 
in the Blue Ridge Mountains are presumably physically well isolated 
from cave populations in the Appalachian Valley at present, and 
because there is no evidence for much dispersal mobility in these tiny 
snails, we must assume that this isolation has prevailed for a long period 
of time. Presumably, however, at one time in the past these populations 
were more or less contiguous. 
The isopod family Asellidae is probably a very ancient freshwater 
group dating back perhaps to the Mesozoic (Birstein 1964). There are 
many genera and numerous subterranean species. Some of the troglo- 
bitic species of Caecidotea undoubtedly have been in subterranean 
groundwaters for a long period of time, but based on the fact that there 
are a number of epigean species in the genus, of which some are appar- 
ently not far removed taxonomically from hypogean species, we suspect 
that the majority of troglobitic species have evolved directly from sur- 
face ancestors. The genus also contains a small number of troglophiles 
or trogloxenes, and some of the stygobionts from the east-central Uni- 
ted States sometimes have vestigial eyes and light pigmentation (Lewis 
and Bowman 1981). In the Greenbrier Valley of West Virginia just west 
of the study area, Caecidotea scrupulosa (Williams), a typical epigean 
species outside karst areas, has apparently recently invaded caves, 
and populations show varying degrees of eye and pigment loss, some- 
times corresponding to the distance these animals live inside caves 
(Steeves 1969). 
The occurrence in subterranean waters of Lirceus is probably more 
recent than that of Caecidotea , inasmuch as species of the former are 
much less common in caves and only two of the 15 described species in 
this genus are troglobites. These two troglobites, which are closely 
related sister species that occupy very delimited ranges in different karst 
areas on opposite sides of Powell Mountain in southwestern Virginia, 
do not appear highly specialized morphologically for a cave existence or 
far removed traxonomically from epigean congeners (Holsinger and 
Bowman 1973, Estes and Holsinger 1976). In the Ward Cove karst of 
Tazewell County, an undescribed species of Lirceus with tiny eyes 
inhabits several cave streams and their combined resurgence at Maiden 
Spring. Specimens from the spring population are pigmented, whereas 
those from the caves are not. 
Following colonization of subterranean waters, asellid isopods can 
apparently disperse over relatively broad areas through groundwater 
habitats outside of caves and even karst areas. Of the 1 1 troglobites in 
the study area, six are found in more than one drainage basin, and only 
four are known from a single karst area. Caecidotea pricei for example, 
although usually found in caves, has been collected several times in the 
