Balanus glandula

Great Acorn Barnacle

Photos by Susanna Pearlstein, 2004

Size: 14 mm in diameter, 7-8 mm in height. When crowded can be elongate and columnar, (center picture, Chthamalus fissus attached to columnar Balanus glandula).

Range: From Southern California to the Aleutian Islands.

Habitat: Generally found in Chthamalus fissus between low and high tide marks. Attached to rocks, pilings, mussels, floats, shells, kelp, driftwood, boats and crabs backs.

Misidentification: Chthamalus fissus, this is a stretch simple because the two are often found together. C. fissus is smaller, 8 mm in diameter, and has a smooth, oval operculum, whereas Balanus glandula is larger and has deeply ridged plates on the operculum.

Life History: Larva are called naplius, this is the first larval stage characterized by three pairs of appendages, (antennules, antennae and mandibles). After several molts larva enters cypris stage. This stage has all the appendages of naplius stage but additional mouth parts and six pairs of thoracic limbs and a bivalve shell. It is in cypris stage that C. glandula can attach to substrate by secreting a type of cement from the antennules.

Predators: Primarily preyed upon by Pisaster sp. sea stars and Nucella sp. whelks.

Links: http://www.nwmarinelife.com/htmlswimmers/b_grandula.html,

http://www.marine.gov/Updated%20webpages/MMS/chthamalus.html

Suggested Readings: Kozloff E.N. 1973. Seashore Life of Puget Sound, the Straight of Georgia and the San Juan Archipelago. University of Washington Press.

Johnson M.J. and Snook H.J. 1955. Seashore Animals of the Pacific Coast. Dover Publications, Inc.

Prepared by Susanna Pearlstein, 5/04

Specimen found on Evergreen beach