- fish (3 classes)
- amphibians
- reptiles
- birds
- mammals
Features which distinguish the vertebrates from other chordates are:
Fish - 3 classes are extant
Agnatha: jawless fish (oldest vertebrate fossils from 500 million years old)Only the parasitic lampreys and scavenging hagfish survive.Chondrichthyes: cartilaginous sharks and rays. They are characterized by:
- tough skin covered with toothlike placoid scales
- residual bony tissue in the spinal column of sharks
- lack a swim bladder
- asymmetrical tail
- teeth (derived from placoid scales) form continuously in the mouth - older teeth eventually fall out to be replaced
- digestive system ends in a cloaca - a posterior chamber that also recieves the reproductive and excretory tubes. The cloaca in some form is found in all vertebrates.
- lateral line organ is charateristic of all fish runs the length of the body and senses vibrations in the water.
Osteichthyes - body fish
- very diverse group with members expanded into nearly every aquatic niche
- fins in osteichthyes are more refined, increasing maneuverability over sharks, allowing them to dart in and out
- body is covered with scales and numerous mucous glands creating a slimy covering which greatly reduces drag by water friction.
- presence of a swim bladder which serves to adjust vertical position by altering density and improves balance.
- respiration consists of drawing water over capillary rich gills supplied with blood pumped directly from the ventricle of a 2 chambered heart.
- bony fish are thought to have evolved from some kind of air-breathing, freshwater ancestor that had already developed lungs.
