Search
Balanus amphitrite
Common names: Striped barnacle, Purple acorn barnacle
Description:
Balanus amphitrite is white with purple or brown stripes. It is a small, conical, sessile barnacle.
Size:
B. amphitrite is about 1.5 cm in diameter.
Range:
Distributed world-wide in warm and temperate seas. They originated in Southwestern Pacific and Indian Ocean and have been unintentional introduced to the rest of the world.
Habitat:
B. amphitrite are found intertidally in harbors and protected embankments. They will attach to any available hard surface including rocks, pier pilings, ship hull, and oyster shells.
Natural History:
Barnacles are crustacea closely related to shrimps and crabs, however unlike these free living creatures they live out their lives inside hard shells which are firmly attached to a substrate. Once a barnacle has died its empty shell may remain for some time so as to provide a home for other animals. In situations where barnacles are plentiful, the large amount of empty shells can support a vast community of tiny invertebrates such as cryptofauna.
Predators:
One of the main predators of Balanus amphitrite is a snail belonging to the genus Nucella.
Development:
All barnacles are hermaphroditic and undergo a complex metamorphosis. Most hatch as nauplii and soon become cyprid larvae. They have a bivalve carapace and compound eyes. The cyprid attaches to a substrate (rock, wood, etc.) by its first antenna which have adhesive glands. The complex metamorphosis begins once the cyprid attaches itself to a substrate. These dramatic changes include, secretion of the calcareous plates, loss of eyes and transformation of the swimming appendages to cirri. The cirri are specialized paired appendages used to strain incoming water for the small particles on which they feed.
Misidentification:
The giant acorn barnacle, Balanus nubilus is another common barnacle found in the Puget Sound, but the external shell of Balanus amphitrite is lighter in color, smooth, and bluntly pointed at the top.
Miscellaneous:
Barnacles frequently cover entire ship bottoms by settling and growing there. It is possible for the barnacles to become so abundant that they may reduce the speed of a boat by 30%-40%.
Additional Resources:
Anderson, D. T. (1994). Barnacles; Structure, function, development, and Evolution. Chapman & Hall.
Last updated Friday, August 25, 2006, by Lisa Ferrier
