Phylum Agnatha (Jawless Fish)
Organisms include the hagfish and lamprey. These creatures are eel shaped, and in the case of the hagfish, slime producing. The hagfish is the only known organism to possess a skull, yet lack a vertebral column. Their skulls are made of cartilage. The lamprey are known for sucking the blood from other fish and are easily identifiable by their single nostril and 7 gill pores per side.
Chondrichthyes (Cartilaginous)
Chondrichthyes are cartilaginous, meaning they possess skeletal systems made cartilage, rather than bone. Most possess replaceable teeth and have skin covered in derma denticles, which protect against damage and possible parasites. The members of this phylum also have 5-7 gills per side. One well known member of this phylum is the shark.
Osteichthyes (Bony)
These fish possess full skeletal systems. This also helps build the webbed fins that members of this phylum all possess. Fish of this phylum are among the most common creatures of both oceans and freshwater ecosystems. Many such fish are self-fertilizing. One such member is the atlantic blue marlin.