Crustacean
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 Circular crab
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The crustaceans are a large group of arthropods. Lobsters, crabs, shrimp, and barnacles are familiar crustaceans. Most crustaceans live in the water, either fresh water or salt water. Some have moved on land permanently though. Crustaceans that permanently live on land include some crabs, terrestrial hermit crabs, and woodlice.
Most crustaceans are motile. This means they can move by themselves. Some become sessile, like barnacles, which become attached to a support. Some are parasitic, like sea lice, fish lice, whale lice, and tongue worms.
Crustaceans have three major body parts. They are, front to back: head, thorax, and abdomen. Generally, they have two pairs of antennae, two eyes, and three pairs of jaws on their head. Most breathe with gills, although certain land crabs have developed lungs.
Of all the animals, crustaceans are the closest relatives of insects.
Lobsters and crabs have hard outer skeletons, and tend to preserve well as fossils. However, some crustaceans, such as barnacles, have thin shells, and their fossils are quite rare.
