''Megabalanus coccopoma'', the titan acorn barnacle, is a tropical species of

barnacle Barnacles are arthropods of the subclass (taxonomy), subclass Cirripedia in the subphylum Crustacean, Crustacea. They are related to crabs and lobsters, with similar Nauplius (larva), nauplius larvae. Barnacles are exclusively marine invertebra ...

first described by

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

in 1854. Its native range is the Pacific coasts of South and Central America but it is extending its range to other parts of the world.

Description

The titan acorn barnacle is a large species with

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

plates forming a steep-sided cone which grows to a height and width of . The plates are smooth and are fused together. They are pink and are separated by narrow purple or white radii and the aperture at the top is small. In the Pacific Ocean this species can be confused with ''

Megabalanus californicus ''Megabalanus californicus'', the California barnacle, is a species of large barnacle in the family Balanidae. It is native to rocky coasts in the Eastern Pacific Ocean from North California to the Gulf of California. Description ''Megabalanus c ...

'' but that species is a darker colour, has a wider aperture and has wider rays between the plates.

Distribution

The native range of the titan acorn barnacle is the Pacific coasts of Central and South America from

Mazatlán Mazatlán () is a city in the Mexican list of states of Mexico, state of Sinaloa. The city serves as the municipal seat for the surrounding , known as the Mazatlán Municipality. It is located on the Pacific Ocean, Pacific coast across from th ...

, Mexico to the Ecuador/Peru border. It is found growing on rocks and other hard substrates from the low tide mark down to about .

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

specimens of this barnacle have been found in rocks dating back to the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

and it occurred in

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58fouling community Fouling communities are communities of organisms found on artificial surfaces like the sides of docks, marinas, harbors, and boats. Settlement panels made from a variety of substances have been used to monitor settlement patterns and to examine s ...

on the hulls of ships, and appeared in Belgian waters in 1997. It is now also present on the coast of the United States from North Carolina southwards to Florida and in the Gulf of Mexico. It was first seen in Louisiana in 2002 and in Florida, Georgia, South and North Carolina in 2006. It may be extending its range northwards on this coast because higher surface water temperatures allow it to live and reproduce there. It suffered a setback in these areas in the cold winter of 2009–10. It appeared at

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

in 1985 following an

El Niño EL, El or el may refer to: Arts and entertainment Fictional entities * El, a character from the manga series ''Shugo Chara!'' by Peach-Pit * Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things'' * El, fami ...

event in 1982–3 when

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

s were up to above the average. To reach San Diego it is likely to have previously settled in one or more intermediate locations because San Diego is too far from its known range for the larvae to have drifted there in one season. In 2010, it was for the first time recorded in South Africa, on a buoy near the entrance to the

Port of Durban The Port of Durban, commonly called Durban Harbour, is the largest and busiest shipping terminal in sub-Saharan Africa. It handles up to 31.4 million tons of cargo each year. It is the fourth largest container terminal in the Southern Hemisphe ...

; it is likely that the species is already present at other sites on that coast.

Biology

The titan acorn barnacle is a

suspension feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a spec ...

, extending its cirri (modified legs) from the aperture at the top of the shell to catch plankton. As with other barnacles, sexual reproduction involves the passing of sperm along a long slender tube into the mantle cavity of a neighbouring barnacle. Fertilisation is internal and the larvae are

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic. After passing through several stages over the course of about three weeks, they settle and undergo

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

. They are gregarious and tend to settle near others of their species on rocks, on new man made structures such as cables, buoys and the hulls of boats, and also on the shells of

bivalve molluscs Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

References

{{Taxonbar, from=Q3808943 Barnacles Crustaceans of the eastern Pacific Ocean Crustaceans described in 1854 Taxa named by Charles Darwin