Class Agnatha

The Class Agnatha, a group of jawless fish, belong to the phylum chordata, organisms with a notochord. Agnatha comes from the roots a, meaning "without", and gnáthos, meaning "jaw." The number of species is debated but there are about 100 species of jawless fish currently known. As the most primitive members of the vertebrates, agnathans differ from all others in several important respects. First, they lack hinged upper and lower jaws and instead have unhinged circular mouths. They also lack the paired appendages (fins or limbs) that are found in other vertebrates. In addition, the internal skeleton of agnathans is not bony but cartilaginous.

Pacific hagfish are long and tubular in shape, resembling an eel. They are cartilaginous fish that have a flexible skeleton. They have a relatively short head with a pointed snout and barbels around the single rostrum and mouth. They have no true fins but do have a very long dorsal and ventral fin fold. They have 10-14 gill pores on the anterior portion of the body. They do not have true jaws. Their mouth is a ring of sensitive short tentacles. Their tongue has two pairs of rasps that are used for pulling and tearing. Skin pores on both sides of their body through which slim is ejected run the length of their lateral line. The coloration of these fish can be tan, gray, dark brown, brownish-red, or tinted with blue or purple. Their ventral side is lighter color. They grow up to 18.4 inches and weigh from 1.8-3.1 pounds.

The sea lamprey is an aggressive parasite with a toothed, funnel-like sucking mouth and rasping tongue, which is used to bore into the flesh of other fishes to feed on their blood and body fluids. Sea lamprey are generally 12 to 20 inches long and they weigh 8 to 13 ounces each. Sea lamprey are grayish blue-black with metallic violet on their sides with silver white coloration on the underside.