Barnacles - sessile crustaceans

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.

Geogr. Range:  Aleutian Islands to northern Baja
Synonyms:
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.

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.

Geogr. 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.

Image: Mytilus californianus (across top & left)

Megabalanus californicus  (Pilsbry, 1916)
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Balanidae

Acorn barnacle to 30 mm diameter, shell plates with longitudinal red and white stripes; mantle margin with orange, blue, yellow, & red - most colorful local barnacle.

Common but patchy; low intertidal zone and subtidal on rocky substrate; most frequently seen in clusters on buoys & pilings.

Geogr. Range: northern California to Gulf of California
Synonyms: Balanus tintinnabulum californicus
Similar species:  

Chthamalus spp.
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Chthamalidae

Acorn barnacle; small, brownish white to gray; to 8 mm diameter, 6 ~equal size shell plates, smoother than Balanus glandula; lacks calcareous basal plate. Two local species (C. dalli & C. fissus) cannot be distinguished easily in the field.

Abundant, high to upper mid-intertidal zones, exposed outer coast to protected bays.

Geogr. Range: Chthamalus dalli Alaska to San Diego; Chthamalus fissus: San Francisco to Baja
Synonyms:
Similar species: C. fissus sometimes possesses a slit-like aperture (arrow); setae at ends of 2nd cirri coarsely bipectinate. Setae at ends of 2nd cirri in C. dalli are finely bipectinate.

Image: form with slit aperture (arrow) is Chthamalus fissus.

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.

Geogr. Range: San Francisco to Cabo San Lucas (Baja)
Synonyms: 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.

Pollicipes polymerus Sowerby, 1833
Phylum Arthropoda, Subph. Crustacea, Class Thecostraca, Subcl. Cirripedia, Order Thoracica, Family Scalpellidae

Gooseneck barnacle; to 80 mm tall; muscular fleshy base attaches animal to hard substrate.

Abundant; mid-intertidal zone on exposed outer coast; often associated with beds of the mussel, Mytilus.

Geogr. Range: British Columbia to northern Baja
Synonyms: Mitella polymerus
Similar species: Other gooseneck barnacles such as Lepas are oceanic and attach to floating logs, net floats, & other objects that sometimes wash ashore.

Image: Mytilus californianus around barnacles; mussel form of Lottia pelta  (arrow).