Tetraclita rubescens Darwin, 1854
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Tetraclitidae
Acorn barnacle, shell plates reddish (white in young uneroded individuals) with a thatched appearance; to 30 mm diameter. With only 4 shell plates instead of 6 (as in all other local acorn barnacles).
Common, mid- to low intertidal zones on exposed outer coast.
Geo Range: San Francisco to Cabo San Lucas (Baja)
Tetraclita squamosa rubescens
Similar species: Semibalanus cariosus also has a thatched appearance, but is not reddish and has 6 un-equal shell plates rather than just 4.
Image: small limpets are probably Lottia scabra.