Sharks,dogfish, skates, and rays belong to a class of fishes called Chondrichthyes, which is a division of the superclass Gnathostomata (meaning “jawed mouths”). Also sometimes known as elasmobranchs, sharks and their relatives have a skeleton made of cartilage (hence their common name, cartilaginous fish), a characteristic that distinguishes them from bony fish. Other important features of cartilaginous fish are extremely tough, toothlike scales, and lack of a swim bladder. Jawless fish— lampreys and hagfish—are primitive, eellike fish that make up the order Cyclostomata (meaning “round mouths”), a division of the superclass Agnatha (meaning “without jaws”). In addition to their characteristic round, suckerlike mouths and lack of jaws, cyclostomes also have smooth, slimy skin without scales, and unpaired fins.
Sharks,dogfish, skates, and rays belong to a class of fishes called Chondrichthyes, which is a division of the superclass Gnathostomata (meaning “jawed mouths”). Also sometimes known as elasmobranchs, sharks and their relatives have a skeleton made of cartilage (hence their common name, cartilaginous fish), a characteristic that distinguishes them from bony fish. Other important features of cartilaginous fish are extremely tough, toothlike scales, and lack of a swim bladder. Jawless fish— lampreys and hagfish—are primitive, eellike fish that make up the order Cyclostomata (meaning “round mouths”), a division of the superclass Agnatha (meaning “without jaws”). In addition to their characteristic round, suckerlike mouths and lack of jaws, cyclostomes also have smooth, slimy skin without scales, and unpaired fins.
