Class: Agnatha

OR

Classes: Myxini and Cephalaspidomorphi

Taxonomists used to class the jawless fishes as agnatha, but some taxonomists now divide that class into two other classes: myxini, and cephalaspidomorphi. All jawless fishes have a round, rasping mouth (sometimes also sucker-like) instead of jaws.

Myxini

This is the hagfish: A scaleless, slimy, marine fish with an eel-like body lacking paired fins and bones (though it is still considered a vertebrate--the nerve cord is protected by a tubular notochord). Hagfishes have tentacles around their mouth, and feed on dead or dying fish by scraping off flesh with a rasping tongue. Of the many unusual features of hagfish, one is that they have six hearts! Adult hagfishes are typically about two feet long.

Hagfish. NOAA.

Cephalaspidomorphi

This is the lamprey: A scaleless, marine or freshwater fish with an eel-like body lacking paired fins and bones. Though it lacks bones, it is still considered a vertebrate--the nerve cord is protected by a tubular notochord. Adult lampreys are parasites, attaching themselves to the side of their host with a sucker-like mouth and scraping the flesh away with a rasping tongue. They then suck the fluids and tissues from their host. Adult lampreys are typically about two feet long.

A lamprey attacks a fish. Konrad Schmidt, Native Fish Conservancy.

A lamprey's mouth. Konrad Schmidt, Native Fish Conservancy.