There are a lot of differences between a lamprey and hagfish. The lamprey occurs in the fresh water as well as act a marine. It acts both as a parasite and non parasite. It may grow up to 1 meter, while the hagfish is mainly marine. It acts mainly as a parasite. Its size is up to 1meter. The lamprey has a stout body and less slimy skin. It has ventral mouth and the functional pair of eyes. The hagfish has a feeble body and a more slimy skin. It has a terminal mouth and the degenerative pair of eyes. The lamprey tongue is not well developed. It has larger teeth. The brain is well developed and has separate sexes. The tongue of hagfish is well developed. It has smaller teeth. The brain is not well developed and has no separate sexes and is known as hermaphrodite. The development of lamprey is indirect with the formation of larva. They have 20 cranial nerves and 14 gill slits. The hagfish shows the direct development without the formation of larva. They have 16 cranial nerves and 2 gill slits. The salivary glands secrete an anticoagulant in lamprey and they remove the flesh and suck the blood of fishes. The hag fish has no salivary glands and mainly acts as a scavenger on dead fishes.