Invertebrate Cave Fauna 
131 
strongly against a Paleozoic origin. Although the oldest known isopods 
are recorded from fossils of Pennsylvanian age, these early forms were 
phreatoicideans and not flabelliferans (Schram 1974, 1977). Based on 
fossil evidence, flabelliferan isopods did not appear until the Triassic 
(Schram 1974). Furthermore, the Appalachians did not develop into 
their present form until periods of extensive uplifting, folding, and fault- 
ing occurred in late Paleozoic and early Mesozoic times. “Stable” 
groundwater habitats almost certainly could not have existed in this 
region until post-Triassic times. 
It appears more probable that freshwater cirolanids ancestral to A. 
lira were derived from marine forms in the Late Cretaceous or early 
Tertiary when marine embayments existed on the coastal plain of 
Virginia approximately 100 km east of the Appalachian Valley. Their 
invasion of freshwater habitats would have been followed by their 
migration west into karst areas west of the Blue Ridge. Bowman (1964) 
has also suggested the possibility of an origin along the Atlantic coast 
with subsequent dispersal to the west. But he pointed out that this mode 
of origin would have required a freshwater epigean progenitor, in 
contrast to other troglobitic cirolanids, which are believed to have 
descended directly from marine ancestors. 
Whether its ancestral stock was epigean or hypogean cannot be 
determined, but in view of the evidence given above, it is doubtful that 
A. lira was derived directly from a marine ancestor. It should be noted 
further that, despite the extreme rarity of epigean freshwater cirolanids, 
at least one bona fide freshwater species, Saharolana seurati Monod, is 
recorded from a spring basin in southern Tunisia (see Monod 1930, 
Vandel 1965b). The reduced eyes and association with a groundwater 
outlet of this species suggest that it is preadapted to a subterranean 
existence. A similar stage may have occurred during the evolutionary 
history of A. lira. 
The troglobitic amphipod fauna has probably originated directly 
both from epigean ancestors (e.g., Crangonyx ) and from ancestral 
lineages already living in subterranean waters (e.g., Bactrurus and 
Stygobromus). The family Crangonyctidae, which contains all of the 
troglobitic amphipods in the study area, is widespread over the Holarctic 
region and, like Asellidae, is presumably an ancient freshwater group 
dating back to the Mesozoic (Holsinger 1977, 1978, 1986a, 1986b). 
With the exception of one species from Florida and two or three 
from Europe, troglobitic species of Crangonyx are not far removed 
taxonomically from surface congeners and do not appear to be as highly 
specialized for a subterranean existence as species of Bactrurus and 
Stygobromus (see Holsinger 1969a, 1977; Culver 1976; Dickson and 
Holsinger 1981). Of the 22 described species in the genus, eight are 
troglobitic (or phreatobitic) and two are troglophilic. Most of the 
