Sessilia on an old bucket...

From Wikipedia,


Barnacles (Sessilia) such as the common zeepok (Semibal anus balanoides) is an order of crustaceans. They seem at first sight not on crabs or shrimp, but belong to the rank leg lobsters (Cirripedia). He locks on several surfaces: on wood, on stones, on shells and even on the skin of whales and the shield of sea turtles.


The housing is often white and rock hard. The shape can conical but in dense populations they can grow to high pillars. They consist of a cottage of six lime pictures, with a lid consisting of two lime pictures is formed. The larvae of barnacles don't have any fish and swim around freely. Some barnacles live fully embedded in their host, as in the inside edge of the shell of the whelk (Buccinum baccatus), especially if those inhabited by its secondary occupant: the common hermit crab (Pagurus bernhardus).