Proteus (Laurenti), Or Hypochthon (Merr.), a perennibranchiate batrachian reptile, belonging to the same family as the axolotl and the menobranchus. The skin is naked and slimy, the body elongated and cylindrical, and the tail short, broad, and compressed laterally; the branchial tufts are three pairs, and persistent during life; legs four, rather weak, the anterior three-toed and the posterior four-toed. The common proteus (P. anguinus, Laur.) is about a foot long and half an inch in diameter; it is pale flesh-colored or white, with the branchial tufts bright crimson; the teeth are small and sharp, in both jaws and on the palate; the head triangular, and the snout obtuse; the eyes are very small, and without lids. It is found only in the subterranean waters of some caves of Europe, as in Carinthia and Tyrol, and especially in the Adelsberg cavern in Carniola. The respiration is essentially aquatic by means of the branchial tufts, though it has rudimentary lungs, rises to the surface to swallow air, and can live a short time out of the water, like the menobranchus; its motions by means of the legs are sluggish and awkward, but it swims rapidly and with ease by lateral undulations; when the water of its subterranean retreat becomes low, it buries itself in the mud; the food consists of aquatic worms and insects, and soft-shelled mollusks.
Several local varieties occur, generally referred to the same species; one of these is purplish with yellow spots, and larger, widely extended, and coarsely divided gills; these are described as species of hypochthon by Fitzinger in the Sitzungsberichte of the academy of Vienna for October, 1850. (See Menobranchus.)