Barnacles live only in the sea. They are related to crabs and lobsters.
Barnacles stick themselves to a surface and live there in the same place for their entire adult lives. You usually see them on the beach stuck to rocks, or stuck to the bottom of boats. They eat small sea creatures that drift past them in the water.
Crabs are found all over the world around water, both in the sea and in fresh water. They can range in size from a few centimetres wide to up to four metres wide. They have a very thick outside shell, and people catch them to eat.
Hermit crabs are not actually true crabs, but are distantly related crustaceans. Hermit crabs don't have a shell of their own, so they need to find the discarded shell from another creature to wear. As they grow, they have to find another shell to replace their old one.
Hermit crabs are found all over the world, and many people keep them as pets.
A shrimp, also called a prawn in many countries, is a sea creature that usually grows to a few inches long. They are a very popular food, and can be eaten boiled, fried, barbequed and many other ways, plain or with a sauce. They are quite often cooked whole and you have to remove the head, legs and other inedible parts yourself.
The woodlouse (also called an armadillo bug, carpenter, cheeselog, doodlebug, pill bug, roly-poly, chuggypig, slater beetle, sow bug or gramersow) is a type of crustacean, and is related to the crab and lobster. They eat dead plants and fallen leaves.
Woodlice breathe through gills like fish, which is why you often find them in damp places. Some types of woodlouse can roll themselves up into a tight ball.