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Class - Agnatha

(Jawless Fish)

Did you know the jawless fish are known to be the earliest known vertebrates? Researchers have identified jawless fish to be very ancient like five hundred million years old. Jawless fish are of the group Agatha. Most of the species of  jawless fish are extinct. Two classes of jawless fish that are still living are the hagfish and the blood sucking lamprey. Hagfish live in cold and temperate waters. The hagfish is said to have a braincase but no jaw, the hagfish also have very poorly developed eyes.


The hagfish also lack a nervous system, a spleen, and scales. The hagfish has a circular mouth with rows of teeth. The hagfish spend most of their time in embedded muddy bottoms. The hagfish are scavengers eating through their victims and only leaving the skin and skeleton left of the victim. Hagfish have glands on both sides of their body. Theses glands produce lots of mucoid material, they use this for a defense mechanism. Scientist say the hagfish have no larval stage.


There are twenty species of hagfish. The Atlantic hagfish called Myxine Glutinosa reaches a length of thirty inches. The Pacific hagfish called Eptatretus Stouti has been used for physiological studies. The hagfish is in the phylum chordata.


The blood sucking lampreys lack a nervous system, spleen, and scales. The lamprey’s circular mouth is also lined with rows of teeth like the hagfish. The lamprey’s teeth attach to the prey and it feeds as it’s carried along. The lampreys have anticoagulant in there saliva to keep there victims blood fluid. Some of the fresh water lampreys eat flesh to. The lampreys look like ells but researchers say they are not related. When the lampreys aren’t feeding they swim with undulating movement. The larvae of the lampreys are called ammocoetes. The ammocoetes are about ¼ inches which is about 6mm long. The larvae of the lampreys are transparent.


Some of the interesting facts I found out about the jawless are that the hagfish have no larval stage, and the lampreys larvae are transparent. What I also thought was interesting was that the hagfish spend most of there time in muddy bottoms. The lampreys just swim along side its victim drinking its blood. I thought it was neat that the lampreys have anticoagulant in their saliva to keep there preys blood fluid.

Author: Brooklyn, P

Date Published: April 2006



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