''Balanus glandula'' (North American Acorn Barnacle, Common Acorn Barnacle) is one of the most common

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

species on the

Pacific coast Pacific coast may be used to reference any coastline that borders the Pacific Ocean. Geography Americas Countries on the western side of the Americas have a Pacific coast as their western or southwestern border, except for Panama, where the Pac ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, distributed from the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sover ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

to Bahía de San Quintín near

San Quintín, Baja California San Quintín is a city in San Quintín Municipality, Baja California, located on the Pacific Coast of Mexico. The city had a population of 4777 in 2011. San Quintín is an important agricultural center for Baja California. The city is also an emer ...

. They are commonly found in the upper

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

s, rocks and pier pilings. They can obtain oxygen from both water and air. This acorn barnacle is a moderate-sized one with a diameter of up to . The shell is formed by overlapping plates and has a calcareous basis. It has more the shape of a cylinder than the shape of a cone. The white operculum has heavily ridged walls. It can live up to ten years. It has been intensely studied in recent years as a model species for linking

physical oceanography Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters. Physical oceanography is one of several sub-domains into which oceanography is divi ...

and

population genetics Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...

(or

phylogeography Phylogeography is the study of the historical processes that may be responsible for the past to present geographic distributions of genealogical lineages. This is accomplished by considering the geographic distribution of individuals in light of ge ...

) surveys. This species was introduced to the shores of

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

in the 1960s, and has become an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

, displacing other barnacles and mussels.

References

Barnacles Crustaceans of the eastern Pacific Ocean Crustaceans described in 1854 Taxa named by Charles Darwin {{Maxillopoda-stub