''Amphibalanus eburneus'', the ivory barnacle or American acorn barnacle, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of acorn

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 ...

in the family

Balanidae The Balanidae comprise a family of barnacles of the order Balanomorpha. As a result of research published in 2021 by Chan et al., the members of the family Archaeobalanidae were merged with this family. Genera These genera belong to the family B ...

. It occurs on the east coast of

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 ...

, the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

and

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

Description

The ivory barnacle is a medium-sized, cone-shaped

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

barnacle with a white test composed of fused plates. It has a diamond-shaped operculum protected by a hinged lid formed from two triangular halves each consisting of two plates, a tergum and a scutum. It can grow to a height of but most individuals are much smaller. This barnacle can be confused with the white bay barnacle (''

Balanus improvisus ''Amphibalanus improvisus'', the bay barnacle, European acorn barnacle, is a species of Sessilia, acorn barnacle in the Family (biology), family Balanidae. Description ''Amphibalanus improvisus'' has a smooth white or pale grey conical calcareou ...

'') but that species is smaller, only growing to a height of . Another similar species is the striped barnacle (''

Balanus amphitrite ''Amphibalanus amphitrite'' is a species of acorn barnacle in the Balanidae family. Its common names include the striped barnacle, the purple acorn barnacle and Amphitrite's rock barnacle. It is found in warm and temperate waters worldwide. Desc ...

'') but that has vertical pink lines on the test.

Distribution and habitat

The native range of the ivory barnacle extends from

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

to the

and

but it has extended this range as a result of

fouling Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surf ...

the bottoms of ships and because its larvae are sometimes transported in ballast water. It was first seen in

Pearl Harbor Pearl Harbor is an American lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. It was often visited by the Naval fleet of the United States, before it was acquired from the Hawaiian Kingdom by the U.S. with the signing of the Re ...

, Hawaii in 1929 and is now common in all the main islands. It is found, sometimes in great numbers, from low tide mark to depths of attached to hard surfaces including rocks,

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

shells, pilings,

jetties A jetty is a structure that projects from land out into water. A jetty may serve as a breakwater, as a walkway, or both; or, in pairs, as a means of constricting a channel. The term derives from the French word ', "thrown", signifying somet ...

and other man-made structures, ships' hulls and the roots of the red mangrove (''

Rhizophora mangle ''Rhizophora mangle'', the red mangrove, is distributed in Estuary, estuarine ecosystems throughout the tropics. Its Vivipary, viviparous "seeds", in actuality called propagules, become fully mature plants before dropping off the parent tree. Th ...

'').

Reproduction

Ivory barnacles tend to aggregate with others and form dense populations. Each one is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

but cross fertilisation takes place when an individual protrudes its long penis and inserts it into the operculum of an adjoining individual where eggs have already developed. Sperm is deposited there, and the fertilised eggs are brooded in the mantle cavity. On hatching, the larvae are expelled into the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

and become

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic. They pass through six naupliar stages and one cyprid stage over the course of one to two weeks. The nauplii feed on

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

but the cyprid larvae do not feed. They search out sites for settlement, possibly following chemical cues from already established adults or testing the substrate for suitability. Once settled, they cement themselves by their heads to the surface and undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

into juvenile barnacles.

References

External links

* {{Taxonbar, from=Q2880553, from2=Q13366379 Barnacles Crustaceans of the Atlantic Ocean Crustaceans described in 1841 Taxa named by Augustus Addison Gould