CRUSTACEA/MALACOSTRACA
Lobsters, crabs, shrimp, and isopods are members of the class Crustacea.

Among the 32,000 species of crustaceans worldwide, many live in marine or fresh water, while few live on land.

Common features of crustaceans include:

• Division of the body into head, thorax, and abdomen
• Two pairs of antennae
• Two pairs of maxillae for food gathering
• Larva with only rear appendages
• Appendages with two jointed branches at their ends

Most crustaceans use gills (somewhat differently constructed from fish gills) for gas exchange to obtain oxygen in water. Lobsters employ their two sets of antenna to feel objects and to sense chemicals.

In front of their four pairs of walking legs, the pinching claws, or chelipeds, of lobsters hold food items and serve as defense tools.