| A | B |
|---|
| chordate | The phylum whose members have a notochord and a nerve chord. |
| vertebrae | The bones that make up the backbone of an animal. |
| notochord | A flexible rod that supports a chordate's back. |
| ectotherm | An animal whose body does not produce much internal heat. |
| cartilage | A flexible, strong tissue that is often softer than bone. |
| endotherm | An animal whose body controls and regulates its temperature by controlling the internal heat it produces. |
| fish | An ectothermic vertebrate that lives in the water and has fins. |
| swim bladder | An internal gas-filled organ that helps a bony fish stabilize its body at different body depths. |
| buoyant force | The force that water exerts upward on any underwater object. |
| amphibian | An ectothermic vertebrate that spends its early life in water and its adulthood on land, returning to water to reproduce. |
| habitat | The specific environment in which an animal lives. |
| atrium | An upper chamber of the heart. |
| ventricle | The lower chamber of the heart, which pumps blood out to the lungs and body. |
| reptile | An exothermic vertebrate that has lungs and scaly skin. |
| urine | The watery fluid in which the wastes produced by an animal's cells are excreted. |
| fossil | The hardened remains or other evidence of a living thing that existed in the past. |
| sedimentary rock | Rock formed from hardened layers of sediments--particles of clay, sand, mud, or silt. |
| paleontologist | A scientist who studies extinct organisms, examines fossil structure, and makes comparisons to present-day organisms. |
