| A | B |
|---|
| chordate | any animal having, at some stage in development, a notochord, a hollow nerve cord, pharyngeal slits, and tail |
| notochord | flexible skeletal support rod embedded in an animal's back |
| endoskeleton | internal skeleton built of bone or cartilage |
| gill | respiratory organ of aquatic animals that allows breathing underwater |
| countercurrent flow | flow of water opposite that of the flow of blood in a fish's gills |
| lateral line | sensory system in fish that allows them to sense distant movements in the water |
| operculum | protective bony plate that covers a fish's gills |
| ray-fin | fan-shaped arrangement of bones in a fish's fin |
| swim bladder | buoyancy organ that helps fish to swim at different depths in the water |
| lobe-fin | paired limb-like fine that is round in shape |
| tetrapod | vertebrate with four limbs |
| amphibian | vertebrate that can live on land and in water |
| tadpole | aquatic larva of frogs or toads |
| amniote | vertebrate whose embryo or fetus is enclosed by a thin, tough membranous sac |
| keratin | protein that binds to lipids inside a skin cell, forming a waterproof layer within the skin |
| amniotic egg | waterproof container that allows an embryo to develop out or water and externally from the mother without drying out |
| placenta | organ that develops in female mammals during pregnancy and carries nutrients from the mother to the embryo |
