Any of about 30 species of primitive jawless fishes in two families of the class Agnatha.
The Myxinidae are found in every ocean; the Eptatretidae are found everywhere but the North Atlantic. Hagfishes are eel-like, scaleless, and soft-skinned and have paired thick barbels on the end of the snout. Species grow to 16–32 in. (40–80 cm) long. They have a cartilaginous skeleton. The mouth is a slitlike, sucking opening with horny teeth. Found in cold seawater, to depths of over 4,000 ft (1,200 m), they habitually lie buried in burrows on soft bottoms. They eat invertebrates and dead or crippled fishes, and may bore their way into the bodies of fish caught on lines or in nets and eat the fish from the inside. They secrete extraordinary amounts of slime when handled. See also lamprey .