Notochord
a cartilaginous skeletal rod supporting the body in all embryonic and some adult chordate animals.
Vertebrae
Organisms with a spinal chord
Ectotherm
an animal that is dependent on external sources of body heat. (cold-blooded)
Endotherm
(of an animal) dependent on or capable of the internal generation of heat. (warm-blooded)
Endoskeleton
An internal skeleton
Exoskeleton
A body covering, typically made of chitin, that provides support and protection
Swim bladder
An internal gas-filled organ that helps a bony fish stabilize its body at different water depths.
Placenta
A structure that allows an embryo to be nourished with the mother's blood supply
Marsupial
A mammal, such as a koala, kangaroo, or opossum, whose young complete their embryonic development inside a maternal pouch called the marsupium.
Monotreme
A mammal that lays eggs
Archaeopteryx
An intermediate fossil that shows both reptile and bird characteristics.
Diaphragm
A large muscle located at the bottom of a mammal's rib cage that functions in breathing
Alveoli
(singular alveolus.) Tiny sacs, with walls only a single cell layer thick found at the end of the respiratory bronchiole tree. Alveoli are the site of gas exchange in the respiratory system.