Seanet Mid Intertidal

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Semibalanus cariosus (Pallas, 1788)
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Archaeobalanidae

Acorn barnacle; white to gray; to 60 mm diameter with cascading longitudinal ribs resembling a thatched roof; 6 unequal-size shell plates.  Walls permeated with longitudinal channels in irregular rows.

Common, mid- to low intertidal zones; exposed outer coast.

Geo Range: Bering Sea to Morro Bay (central California)
Synonyms: Balanus cariosus
Similar species: Tetraclita is similar in size & also has a thatched appearance but it's usually red and has only 4 shell plates rather than 6.

Mytilus californianus (across top & left)