Acorn barnacle species can be difficult to identify in photographic monitoring, but Balanus glandula can be distinguished from Chthamalus fissus/dalli by its larger size (to 22 mm), whiter color, and diamond-shaped operculum. Natural HistoryĪcorn barnacles, Chthamalus fissus/dalli and Balanus glandula, typically dominate the high intertidal zone along the western coast of North America. Juvenile Semibalanus cariosus can be distinguished by the margins of the opercular plates. The exoskeleton plates are generally more smooth and fragile. glandula by the shape and margins of the opercular plates. Synonymsīalanus crenatus typically occurs subtidally, but is occasionally present in the very low intertidal and can be distinguished from B. glandula: abundant on rocks, pier pilings, and hard-shelled animals within the high and middle intertidal zones of bays and the outer coast from the Aleutian Islands (Alaska) to Bahía de San Quintín (Baja California) (Morris et al. dalli is found from Alaska to San Diego California (Morris et al. fissus extends from San Francisco, CA to Baja California C. fissus/dalli: common on rocks, pier pilings, and hard-shelled organisms, high and upper middle intertidal zones. These species are virtually indistinguishable in the field.ī. fissus/dalli: small barnacle, up to 8 mm in diameter. Phylum Arthropoda, class Maxillopoda, order Sessilia Previous Species | Google image results | Next SpeciesĬ. The giant acorn barnacle is preyed upon by the ochre star ( Pisaster ochraceus).Chthamalus/Balanus (Acorn Barnacles) Chthamalus fissus (Darwin 1854), Chthamalus dalli (Pilsbry 1916), Balanus glandula (Darwin 1854) Some fish species also depost eggs in these empty casings. Thatched barnacles also have beak-like terga, and can reach 6 cm in diameter.Įmpty casings left behind by dead giant acorn barnacles often become hiding places for other animals, such as small and juvenile fish, the pygmy rock crab ( Glebocarcinus oregonensis), and the Pacific red octopus ( Octopus rubescens). Large thatched barnacles ( Semibalanus cariosus) that have undergone erosion and lost their heavy ribbing and finger-like base projections or thatching may be confused with this species. Its range extends from southern Alaska to Baja California, Mexico. Individuals often also grow on one another. It inhabits the intertidal and subtidal to 90 m deep, where it grows on rocks and pilings and prefers areas with strong currents or waves. This barnacle tends to aggregate into clusters and can form large reef-like formations, but may also be found singly. Younger individuals start off with ribbed plate exteriors, but these ridges usually wear away with age. Flashes of bright yellow, orange, or purple tissue are visible inside when these operculum plates open during feeding. If an individual is not large enough for its identity to be obvious, other features can be used to identify this species: it has a broad opening (aperture) in relation to its base, its aperture edge is jagged and rough, its exterior is often heavily worn and eroded, and its terga (interior movable plates that form the operculum) are beak-shaped and extend out of the aperture. At a maximum diameter of 15 cm (equivalent to half a foot), the giant acorn barnacle is possibly the largest barnacle species in the world, and is definitely the largest in North America.
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