Barnacles encrusting wood in Florida, USA. (summer 2009)

The crustaceans are a large group of arthropods that inhabit marine, marginal marine, freshwater, and terrestrial habitats. The crustaceans include crabs, lobsters, shrimp, crayfish, barnacles, ostracods, and other organisms. The oldest fossil crustaceans are in the Cambrian. The group experienced a significant radiation in the oceans during the Mesozoic Marine Revolution.

The organisms shown above are barnacles that are encrusting wood on a marine beach at Cayo Costa Island, Florida. The wood is from a tree killed in late summer 2004 by Hurricane Charley. Barnacles are sessile, benthic, filter-feeding, marine crustaceans that are obligate hard substrate encrusters. They are particularly common in intertidal, rocky shore environments. They can tolerate subaerial exposure during low tides but have to be in water at least occasionally. When submerged, they extend their feathery limbs to filter feed. The barnacle body is enclosed in a small, cinder cone volcano-shaped carapace composed of overlapping calcareous plates. Fossil barnacles first appear in Cambrian rocks.

These barnacles are a mix of striped acorn barnacles, Balanus amphitrite (Darwin, 1854) and ivory acorn barnacles, Balanus eburneus Gould, 1841.

Striped acorn barnacles are relatively small and have a light-colored carapace with thin, purplish-colored stripes. This species is not native to Florida. Based on its fossil distribution, Balanus amphitrite is apparently native to the Indian Ocean and the southwestern Pacific Basin. It is now globally distributed in tropical and temperate, shallow marine environments. The species' geographic distribution is so widespread in modern seas as a result of human activity - the barnacles have frequently attached to ships that travel across entire ocean basins.

Ivory acorn barnacles are larger and have a white carapace with obvious plate boundaries. This species is native to Florida. It is known from the Caribbean Sea, the Gulf of Mexico, and along North America's Eastern Seaboard.

Classification: Animalia, Arthropoda, Crustacea, Maxillopoda, Cirripedia, Sessilia, Balanidae

Locality: marine beach at the southern tip of Cayo Costa Island, Gulf of Mexico coast of southwestern Florida, USA (vicinity of 26° 36' 48.74" North latitude, 82° 13' 19.91" West longitude)

More info. at: en.wikipedia.org/wiki/Crustacean and en.wikipedia.org/wiki/Barnacle and en.wikipedia.org/wiki/Ivory_barnacle and