Fish (Subphylum Vertebrata)

What is a Fish? They can be roughly defined as: Aquatic vertebrates. Possess scales. Possess fins. Maintain pharyngeal gills.

Classification of Fish Jawless Fish

Jawless Fish (Agnathans) The lampreys and the hagfish! They both lack jaws!

Hagfish (MARINE) Perhaps the most primitive vertebrate. Technically not vertebrates since they lack vertebrae. Possess a skull however. Their eyes are under the skin. “No eyes” They lack paired fins. Most verts have paired appendages: fins  limbs. Detritivores/scavengers.

Lampreys (MARINE and FRESHWATER) Also lack paired fins. Have a massive sucker which surrounds the mouth. Possess a sharp tongue and circular rings of teeth. Often ectoparasites of other fish as adults. Have vertebrae and fully developed eyes.

Cartelagenous Fish (Class Chondrichthyes) Have skeletons made of cartilage. Most have tooth-like scales covering their skin as well. Have 5 to 7 gill slits. Serial replacement teeth: Teeth move up and then fall out like on a conveyor belt. Give birth to eggs or to live young.

They are ancient and highly successful predators!!! Skates and rays are highly modified sharks. Dorsoventrally flattened. Swim by flapping large pectoral fins. 2 Major groups of Chondrichthyes. Elasmobranchs: Sharks, skates and rays. Holocephalons: Ratfish.

Bony Fish (Class Osteichthyes) These fish have skeletons or part of their skeletons made of bone A more specialized jaw. Segmented fin rays. A swim bladder: Regulates buoyancy. An operculum: A covering over the gills.

There are two main groups of osteichthyes. Actinopterygii: Ray finned fishes. Most of the fishes we see today. Well developed swim bladder. Fins with ray-like appearances. Sarcopterygii: Fleshy finned fishes. The coelacanth and lungfish. Evolved into tetrapods. Fins have extensions of muscle and bone.