Only one group of crustaceans are sessile, the barnacles. Their appearance is so special that many people do not realize that they are crustaceans. Because they make shells, many people rather associate them with the totally unrelated molluscs. However, inside the shell there really is a crab that uses its legs to filter food rather than walk on or swim like other crustaceans.
Barnacles are found in abundance on the seashore, but larger individuals occur deeper. It is a bit of a problem to find a mate when one is sessile. The barnacles solve this by having the world´s largest penis relative to their body size. The eggs and larvae then drift away with ocean currents to find new sites to settle.
The most common species is Semibalanus balanoides and can be found on rocky seashores all around Iceland.