Barnacles look like molluscs with shells but barnacles are crustaceans. Before they become adults, they look similar to shrimps. As adults they are glued to rocks and other solid structures in the sea. They lie on their back with their legs poking outwards. Their protective skeleton that looks like a shell is made up of plates.
In the middle of the round skeleton are some plates that can be moved like a trapdoor. The legs can be pushed out. They have feathery looking legs that they use to beat the water. They can extract and eat the microscopic food particles from this stream of water.
Besides living on rocks, they can cement themselves to turtle shells, some whales, ships, boats and other structures built by people in the sea. For boats and ships to move properly through the water, hulls are treated so barnacles and other sea creatures can’t grow.
Dead barnacles lose the plates that cover the centre of the skeleton. They look like miniature hollow volcanoes.