White Acorn Barnacle
The White Acorn Barnacle (Balanus glandula), is one of the most common barnacle species on the Pacific coast of North America. It is widely distributed from the coast of Alaska to the border between California and the Mexican state of Baja California. They are commonly found in intertidal waters on mussels, rocks and pier pilings.
It is moderately sized with a length of 0.6 to 0.8 inches. The shell is formed by overlapping plates. It is shaped more like a cylinder rather than a cone. The white operculum has heavily ridged walls. It can live up to ten years.
This barnacle has been intensely studied in recent years as a model species for linking physical oceanography and population genetics surveys. This species has also been introduced to the coastal waters of Argentina within the last 30 years. It has become invasive and has since displaced other barnacles and mussels.