Crustaceans constitute the most diverse group of ocean-living animals on Earth.
They are a type of arthropod.
About 50,000 species of crustacean have been recognized.
Lobsters, crabs and shrimp are crustaceans.
Most crustaceans live in marine or freshwater habitats, but some, such as woodlice, live on land.
The body of a crustacean is made up of a head, a thorax and an abdomen.
The thorax and abdomen may be fused together to form a trunk.
Crustaceans usually have a carapace, or thick shield, that is made up of parts of the exoskeleton. The carapace covers the thorax and abdomen (trunk).
A crustacean has two pairs of antennae and may have claws.
In some crustaceans, the legs are adapted for swimming and are known as swimmerets.
The earliest crustacean fossils that have been found are over five hundred million years old.