Marine Life‎ > ‎California‎ > ‎Invertebrates‎ > ‎


Barnacles look like bivalves, but are actually crustaceans like crabs and shrimp.  They extend out frilly appendages to catch plankton and draw it back into their shells.

Acorn Barnacle

Balanus crenatus

(1,3: San Carlos Beach, Monterey / 2: Monterey State Beach, Monterey)


Menesiniella aquila

(1-2: San Carlos Beach, Monterey)

California Barnacle

Megabalanus californicus

(1: San Carlos Beach, Monterey / 2: Lovers Cove, Monterey)

The first one is hitching a ride on an Ida's miter; the second is on a turban snail.  California barnacles can grow to 2" - the same size as either snail full-grown.  I'm not sure what'll happen when the barnacles outgrow their snails.

Giant Acorn Barnacle

Balanus nubilus

(1,4,7-8: San Carlos Beach, Monterey / 2-3: Monterey State Beach, Monterey / 5-6: Lovers Point, Monterey)

Has a wider aperture than Menesiniella aquila, relative to its size.

Pink Acorn Barnacle

Tetraclita rubescens

(1: Whaler's Cove, Point Lobos)

Juvenile Barnacles

Juvenile barnacles are free-swimming and almost transparent:
(1: San Carlos Beach, Monterey)

When they grow up, they settle down and never move again.  But sometimes they pick unfortunate locations, like on this bat star:
(1: San Carlos Beach, Monterey)