Lampreys and Hagfish are primitive types of fish, belonging to the taxonomic CLASS AGNATHA and Order Cyclostomata
Class Agnatha, probably the first class in the subphylum Vertebrata, consists of marine animals apparently similar to fish but with some very noticeable differences. The agnathans lack both jaws and paired fins.
- They have a sucking mouth.
- The cartilaginous skeleton (not bones, but a softer material called cartilage) is essentially a reinforced notochord.
- Skin is smooth, lacking scales.
- They do not have fins as found in cartilaginous or bony fish.
- They lack the ability to regulate body temperature.
- The heart is two chambered.
- They typically have a single nostril.
- Family Petromyzontidae.
- They have seven pairs of gills, each open separately.
- They have a pineal eye.
- The sexes are separate.
Sea lampreys are blood-sucking parasites. They attach themselves to the skin of fish by their mouths (horny teeth), and then rasp through the skin of the host. Lampreys have an anticoagulant in the saliva that keeps the blood of the victim fluid. Some freshwater lampreys eat flesh as well as blood. Lampreys lack a sympathetic nervous system, a spleen, and scales. Lampreys resemble eels in external appearance and, although not related to the true eels, are sometimes called lamprey eels. The marine lampreys normally migrate into freshwater to spawn, and some populations have become landlocked in freshwater.
- Belong to the Family Myxiniformes.
- These are marine animals.
- They may be hermaphroditic or two sexed.
- They have between 5 and 15 pairs of gills.
- They lack a pineal eye.
- They have an internal nasal opening.
Hagfish are primitive marine fish of worldwide distribution in cold and temperate waters. Its skeleton, of cartilage rather than bone, has a braincase, but no jaw. The circular sucking mouth also has rows of horny teeth, much like the lampreys. There is a single nostril and the eyes are poorly developed. Hagfish have a notochord a supporting structure found in higher vertebrates only in the embryo.
Hagfish spend a lot of time embedded in muddy bottoms. They are mainly scavengers, but also parasitize slow-moving fishes, eating their way into the victim's body and leaving only the skin and skeleton. Hagfish have glands on either side of their bodies that produce large quantities of mucous. It is thought that this is a defence mechanism.