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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.
Semibalanus balanoides (common barnacle, common rock barnacle, or northern rock barnacle) is a common and widespread boreo-arctic species of acorn barnacle. It is common on rocks and other substrates in the intertidal zone of north-western Europe and both coasts of North America .
Most barnacles are encrusters, attaching themselves to a hard substrate such as a rock, the shell of a mollusc, or a ship; or to an animal such as a whale (whale barnacles). The most common form, acorn barnacles, are sessile, growing their shells directly onto the substrate, whereas goose barnacles attach themselves by means of a stalk. [8]
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]
Sessilia is an unranked clade of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked or goose barnacles. [3] Sessilia is divided into two orders.
Perforatus (South European Acorn Barnacle, Red-striped Acorn Barnacle) is a genus of acorn barnacles in the family Balanidae. There is one described species in Perforatus , P. perforanus . from Mykonos Island, Greece [ 1 ] [ 2 ] [ 3 ]
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]
Balanidae Leach, 1817 (acorn barnacles) Bathylasmatidae Newman & Ross, 1971; Catophragmidae Utinomi, 1968; Chelonibiidae Pilsbry, 1916 (turtle barnacles) Chionelasmatidae Buckeridge, 1983; Chthamalidae Darwin, 1854 (star barnacles) Coronulidae Leach, 1817 (whale barnacles) Elminiidae Foster, 1982 [4] Pachylasmatidae Utinomi, 1968; Pyrgomatidae ...