Aquatic vertebrates bearing fins rather than walking limbs.
Locomotion is achieved by body undulations and/or independent fin
movements. Respiration involves gills. Water enters through the
mouth and passes out through two or more gill slits. The skin of most fish is
covered in denticles or scales.
There are three recognized classes of fish:
Cyclostomata = Jawless fish - hagfish, lampreys & relatives A small group of primitive eel-like fishes lacking a jaw and pairedfins, but with a cartilagenous skeleton.