What is a crustacean?

A crab is a crustacean

Crustaceans live mostly in the ocean or other waters and include creatures like shrimps, lobsters, crabs and barnacles.

Crustaceans have a hard, external shell which protects their body. They have a head and abdomen. The head has antennae which are part of their sensory system. The abdomen includes the heart, digestive system and reproductive system.

The abdomen also has appendages, such as legs, for crawling and swimming. Many crustaceans also have claws that help with crawling and eating.

In contrast with other members of the phylum Arthropoda, most notably insects, crustaceans have not been very successful on land. This is because crustaceans lack a waxy, water-tight cuticle. They also have gills for respiration. Gills function best in water, and only a few species have adapted them for use on land.