snail darter, a small, rare fish, Percina tanasi, discovered by a zoologist who was snorkeling in the Little Tennessee River upstream from the projected Tellico Dam. Dam opponents fought successfully to include the darter on the Endangered Species List in 1975 (see endangered species), and the dam was halted. In 1978, the Supreme Court sided with environmentalists, but Congress declared the fish nonendangered and the Tellico was built. Snail darters are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Percomorphi, family Percidae.