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

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 ...

first described by

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...

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 or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

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'' 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 state of Sinaloa. The city serves as the municipal seat for the surrounding ''municipio'', known as the Mazatlán Municipality. It is located at on the Pacific coast, across from the southernmost tip of ...

, 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 preserved ...

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

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

and it occurred in

Baja California Baja California (; 'Lower California'), officially the Free and Sovereign State of Baja California ( es, Estado Libre y Soberano de Baja California), is a state in Mexico. It is the northernmost and westernmost of the 32 federal entities of Mex ...

in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million 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 Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the List of United States cities by population, eigh ...

in 1985 following an

El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date L ...

event in 1982–3 when sea surface temperatures 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 a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, 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 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. 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 or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

. 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 (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

References

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