Acorn Barnacle
Balanus glandula
Summary 3
Balanus glandula is one of the most common barnacle species on the Pacific coast of North America, distributed from the U.S. state of Alaska to Bahía de San Quintín near San Quintín, Baja California. It is commonly found in intertidal waters on mussels, rocks and pier pilings.
Description 4
A sessile (acorn) barnacle in which the rostrum overlaps the rostrolateral wall plates on either side of it, the tips of the terga are not drawn out into a beak, the lines of contact between the terga and scuta are sinuous, and the interior of the base of the shell has numerous centripetal ridges. The scuta have a diagonal line of pits. The inner surface of the scuta and terga is black, and especially in small individuals this shows through to the outside as a dark patch in the center of the scutum where the inner surface is excavated into a deep pit and the scutum is thin. The six wall plates are solid, not filled with hollow longitudinal tubes (except in some young individuals), and do not have fingerlike projecting spines pointing downward. The base is calcified and leaves a calcium deposit on the rock when removed (photo) An extremely common intertidal species, especially in the upper half. Diameter to 2.2 cm, but usually 1.5 cm or smaller. The height is usually about equal to the diameter, unless the barnacles are so crowded that they grow very tall and thin (photo). Walls usually white or grayish white, may have longitudinal ribs (which are often eroded away except in small individuals).
Habitat 5
B. glandula occurs in the high and mid-intertidal, attached to rock or other hard surfaces -- artificial (pilings, floats) or biological (other organisms). They’re common in the exposed outer coast, as well as in bays and estuaries. (Morris et al., 1980)
Life cycle 6
Mothers brood eggs, which are released into the water as nauplius larvae. These planktonic larvae undergo five molts to become a non-feeding cypris with six pairs of legs. Cyprids attach to suitable substrate (avoiding potential predators or competitors) and metamorphose into the adult form. They reach adult size in about two years. The entire lifespan is about 10 years. (Cowles et al., 2002)
Trophic strategy 7
Filters food (plankton and edible detritus) from the water during high tide, using it’s cirri (6 pairs of thoracic appendages).
Sources and Credits
- (c) Joshua Tewksbury, some rights reserved (CC BY-NC-SA), uploaded by Joshua Tewksbury
- (c) Rebecca Johnson, some rights reserved (CC BY-NC), uploaded by Rebecca Johnson
- Adapted by Marisa Rafter from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Balanus_glandula
- (c) Rosario Beach Marine Laboratory, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10455183
- (c) Soulanille, Elaine, some rights reserved (CC BY-SA), http://eol.org/data_objects/17763707
- (c) Soulanille, Elaine, some rights reserved (CC BY-SA), http://eol.org/data_objects/17763708
- (c) Soulanille, Elaine, some rights reserved (CC BY-SA), http://eol.org/data_objects/11290438
