Lampreys and Hagfishes

Lampreys and hagfishes are unusual, jaw-less fish that comprise the order Cyclostomata, so named because of the circular shape of the mouth. The 41 species of lampreys are in the superfamily Petromyzontoidea, while the approximately 35 species of hagfishes and slime hags are in the superfamily Myxinoidea.

Lampreys and hagfishes lack the scales typical of most fish, and are covered with a slimy mucous. These animals have an elongated, eel-like shape, and do not have any paired fins on their sides. Lampreys and hagfishes have gill pouches for ventilation, connected to the external environment by numerous holes or slits on the sides of the body and back of the head. These animals have a simple, cartilaginous skeleton. However, lampreys and hagfishes are divergent in various anatomical characteristics, and each represents an ancient and distinct evolutionary lineage.

Lampreys and hagfishes are living representatives of an ancient order of jawless, fish-like animals that comprise the class Agnatha. Almost all of these jawless vertebrates became extinct by the end of the Devonian period about 365 million years ago. This dieback probably occurred because of competition from and predation by the more efficient, jawed fishes that evolved at that time. However, the ancestors of lampreys and hagfishes survived this evolutionary and ecological change. These distinctive creatures first appear in the fossil record during the Carboniferous period (365-290 million years ago), and are considered to be relatively recently evolved jawless fish. The lack of scales and paired fins in lampreys and hagfishes are traits that evolved secondarily, and are atypical of fossil members of their class, Agnatha.