| A | B |
|---|
| chordates | have a notochord, nerve cord, and gill slits |
| notochord | flexible support for an animal that extends along the upper part of its body |
| hibernation | inactivity during cold weather |
| reptile | live on every continent except Antarctica and in all oceans except those in the polar regions |
| nerve cord | in chordates, its front end usually forms the brain while the remainder forms the spinal cord |
| estivation | inactivity during hot , dry months |
| gill slits | pairs of openings found between the mouth and digestive tube |
| fins | fanlike structures used for steering, balancing, and moving |
| vertebrae | join with cartilage to form the backbone |
| scales | hard, thin, overlapping plates that cover the skin and protect a fish's body |
| crocodile | both the male and the female care for the young |
| endoskeleton | an internal place for the attachments of muscles; also protects internal organs |
| endotherm | an animal with nearly constant body temperature |
| ectotherm | an animal whose internal body temperature changes with the temperature of its surroundings |
| amniotic egg | a complete environment for an embryo |
| cold-blooded | do not maintain a constant body temperature |
| jawless fish | the least developed vertebrates living today |
| boneless fish | another name for jawless fish |
| cartilaginous fish | have skeletons made of cartilage |
| bony fish | have skeletons made of bone |
| ray-finned | fish with pairs of fins that have long, bony rays |
| operculum | a bony plate that covers and protects the gills |
| gills | structure that contains many blood vessels that absorb oxygen and release carbon dioxide |
| milt | a fluid containing sperm |
| amphibians | cold-blooded vertebrates that hibernate in cold weather and estivate in hot, dry weather |
| metamorphosis | a series of dramatic changes some organisms go through from egg to adult |
| tadpole | young frog |
| reptile | cold-blooded vertebrate with thick, dry skin covered with scales |
| venemous | poisonous |
