Over time, some cave-dwelling species adapt specifically for the cave environment. Since caves are dark, there is little advantage for these animals to develop pigmentation or eyes; so evolution of such species eliminates these unnecessary attributes. Such species are known as troglobites. Unlike the troglophiles we've been discussing so far, most troglobites would have a difficult time surviving outside of a cave environment.
Troglobitic invertebrate species are not uncommon, but individual species usually aren't very widespread. The sightless cave crayfish pictured (Orconectes inermis) is one example. Although abundant in one cave managed by the IKC, this species is listed as threatened in Indiana. Its population is monitored for any effects of human visitation.