Barnacle Barnacle A barnacle is a type of arthropod constituting the infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile (nonmotile) suspension feeders, and have two nektonic (active swimming) larval stages. Around 1,220 barnacle species are currently known. The name "Cirripedia" is Latin, meaning "curl-footed". The study of barnacles is called cirripedology. Barnacles are encrusters, attaching themselves permanently to a hard substrate. The most common, "acorn barnacles" (Sessilia), are sessile, growing their shells directly onto the
Bay barnacle and undergo metamorphosis into juveniles. There may be several broods in the year but usually just two in the cooler waters of the Baltic and only one in low salinity environments. Bay barnacle Amphibalanus improvisus, the bay barnacle, is a species of acorn barnacle in the family Balanidae. "Amphibalanus improvisus" has a smooth white or pale grey conical calcareous shell composed of six fused plates. There is an oval or rhombic opening at the top which is blocked by two hinged plates. Adults usually grow to about in diameter and in width though they are sometimes larger than this and