| A | B |
|---|
| invertebrate | an animal that does not have a backbone |
| ganglion | a mass of nerve cells |
| gut | the digestive tract |
| coelom | a body cavity that contains the internal organs |
| open circulatory system | a circulatory system in which the circulatory fluid is not contained entirely within vessels |
| closed circulatory system | a circulatory system in which the heart circulates blood through a network of vessels that form a closed loop |
| segment | any part of a larger structure, such as the body of organism, that is set off by natural or arbitrary boundaries |
| exoskeleton | a hard, external, supporting structure |
| compound eye | an eye composed of many light detectors |
| antenna | a feeler that is on the head of an invertebrate, such as a crustacean or an insect, and that senses touch, taste, or smell |
| metamorphosis | a phase in the life cycle of many animals during which a rapid change from the immature form of an organism to the adult form takes place |
| endoskeleton | an internal skeleton made of bone and cartilage |
| water vascular system | a system of canals filled with a watery fluid that circulates throughout the body of an echinoderm |
