Jawless fish are the most primitive fishes living today. Jawless fish:
There are two categories of jawless fish: hagfish and lampreys.
Hagfish usually feed on dead or dying fish. These fish can be found around the tunnels they dig in muddy bottoms, in moderate depths and cold waters. Scientists only know of about 20 species of hagfish worldwide.
Lampreys are mostly freshwater fish and can be found in temperate regions. Temperate regions lie between the tropics and the polar regions. They breed in rivers and lakes, but some move to the sea as adults. Lampreys depend on other fish for food. Some species of lampreys attach to other fish and suck their blood. They also feed on bottom invertebrates. Worldwide, about 30 species of lampreys exist.