Any of various elongated marine and freshwater fishes lacking a jaw and paired appendages, sometimes thought to constitute the taxon Agnatha. The only extant jawless fishes are the hagfishes and the lampreys.
Any of a class (Agnatha) of fishes with a cartilaginous skeleton, an eel-like body, and a circular, sucking mouth lacking jaws, consisting of the lampreys and hagfishes.
Any of various primitive fish of the class Agnatha that lack jaws. Living jawless fish (lampreys and hagfish) have a long, cylindrical body and a cartilaginous skeleton. The numerous extinct species were often heavily armored and are among the earliest vertebrate fossils known. Jawless fish occupy an intermediate evolutionary position between primitive chordates and jawed fish.