128 
John R. Holsinger and David C. Culver 
It is difficult to speculate on a time of origin for aquatic troglobites. 
Factors that might have been responsible for invasion and colonization 
of subterranean waters by putative ancestors undoubtedly revolve around 
a complex of interacting, interrelated biological and geological pro- 
cesses (see also Barr and Holsinger 1985). Changes in stream gradients 
and flow patterns and diversion of surface streams into underground 
channels by subterranean stream piracy in karst areas have been sug- 
gested as possible factors (Barr 1968, Holsinger et al. 1976, Culver 
1982). All of these geological processes have continued over millions of 
years of erosional history in the Appalachians (see Hack 1969), and 
none is easily identifiable with a given time period. If combined biologi- 
cal and geological-area cladograms can be developed for some of the 
taxa and areas in question, they might prove useful in approximating 
vicariant events that led to the isolation of ancestral populations in 
groundwater habitats. 
One intuitively obvious avenue for the underground invasion of 
aquatic organisms in karst areas would be through springs whose waters 
are the continuation to the surface of cave streams. Many aquatic 
trogloxenes and troglophiles (viz., species of Phagocata, Fontigens, Goni- 
obasis , Gammarus , Lirceus , and Cambarus) inhabit both springs and 
cave streams, and populations are occasionally continuous from a 
spring well upstream into an adjoining cave. Moreover, some troglobitic 
species (viz., in Fontigens , Crangonyx, Caecidotea , and Lirceus ) are 
closely allied taxonomically with congeneric epigean species living in 
surface springs, suggesting close genetic affinities between surface and 
cave forms. The geographic isolation of a population in an underground 
stream could occur if the spring fed by this stream was eliminated by 
erosion or lowering of base level. 
The origin of troglobitic planarians of the genus Sphalloplana is 
somewhat obscure. Of the four species in the study area, two — S. con- 
similis and S. virginiana — are isolated in widely separated karst areas 
and have been assigned to different subgenera (see Kenk 1977). The 
taxonomic position of S. pereoeca is unclear as mentioned earlier, and 
its range may extend far outside the study area. Sphalloplana ehanderli , 
which is widespread but known only from three disjunct localities, is 
probably a “morphological” species. Except for one species with eyes 
and dark pigmentation from a spring in central Japan (see Mitchell 
1968), the anatomy of which has not been studied (Kenk 1977), all other 
members of Sphalloplana are eyeless, unpigmented forms restricted to 
subterranean groundwater habitats, and most of them inhabit caves in 
North America (Kenk 1977, Kawakatsu and Mitchell 1981). 
Despite unresolved taxonomic problems in the genus Fontigens , it 
is obvious from similarities in shell structure that the eyeless, unpig- 
mented cave populations are closely allied morphologically with the 
