The body is noodle-like and often dark in colour, and the skull is bullet-shaped and strongly built. Caecilian heads have several unique adaptations, such as fused skull and jaw bones, a two-part system of jaw muscles, and chemosensory tentacles between the eyes and nostrils. The skin is slimy, with ringlike markings or grooves, and in some species hides scales underneath.

Modern caecilians are a clade, the order Gymnophiona