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Barnacle adults are sessile; most are suspension feeders with hard calcareous shells, but the Rhizocephala are specialized parasites of other crustaceans, with reduced bodies. Barnacles have existed since at least the mid-Carboniferous, some 325 million years ago. In folklore, barnacle geese were once held to emerge fully formed from goose ...
Hemioniscus balani parasitically castrates adults of several species of barnacles, including Semibalanus balanoides, [2] Chthamalus fissus, Chthamalus dalli, and Balanus glandula. Rarely does more than one H. balani parasitize the same host, [ 3 ] but under conditions of heavy infestation, a single barnacle may contain as many as seven H ...
One barnacle may inseminate another up to eight times, and up to six concurrent penetrations may occur. The penis degenerates after copulation, and a new one is regrown the following year. [2] Up to 10,000 eggs may be produced, and they are stored in sacs within the shell cavity. [8] While the eggs are developing, the adult barnacle does not moult.
Rhizocephala are derived barnacles that are parasitic castrators. Their hosts are mostly decapod crustaceans, but include Peracarida, mantis shrimps and thoracican barnacles. Their habitats range from the deep ocean to freshwater. [1] [2] Together with their sister groups Thoracica and Acrothoracica, they make up the subclass Cirripedia. [3]
Acorn barnacle and acorn shell are vernacular names for certain types of stalkless barnacles, generally excluding stalked or gooseneck barnacles. As adults they are typically cone-shaped, symmetrical, and attached to rocks or other fixed objects in the ocean.
Balanus nubilus, commonly called the giant acorn barnacle, is the world's largest barnacle, reaching a diameter of 15 cm (6 in) and a height of up to 30 cm (12 in), [3] and containing the largest known muscle fibres. [4] [5] Balanus nubilus is a northeast Pacific species that ranges from southern Alaska to Baja California. [6]
This acorn barnacle is a moderate-sized one with a diameter of up to 22 mm (0.9 in). [1] The shell is formed by overlapping plates and has a calcareous basis. It has more the shape of a cylinder than the shape of a cone. The white operculum has heavily ridged walls. [1] It can live up to ten years. [1]
Chthamalus anisopoma is a species of intertidal barnacle. Indigenous to the northern Gulf of California, adult Chthamalus anisopoma are found on exposed shores between 0.0 and 2.0 m above mean low tide. The species is typically absent in areas protected from wave splash. [1]