Balanus glandula Darwin, 1854
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Balanidae
Acorn barnacle; white to gray, to 22 mm diameter; 6 unequal-size shell plates, ribbed to smooth depending on location; with calcareous basal plate.
Very abundant, high to mid-intertidal zones, exposed outer coast to protected bays.
Geo Range: Aleutian Islands to northern Baja
Similar species: Chthamalus is smaller & junction of its opercular plates appears more regular; Semibalanus cariosus is larger, has a thatched appearance & usually occurs lower on shore.
Image: smaller brownish-gray barnacles (left of center & lower left) are Chthamalus.