Balanus amphitrite (Darwin, 1854) - striped acorn barnacles encrusting driftwood in Florida, USA (January 2016).

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 striped acorn barnacles that are encrusting a piece of driftwood on a marine beach at Cayo Costa Island, Florida. 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.

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.

Near the top of the photo, some small circular borings in the wood can be discerned - a few of them have visible occupants. These holes were made by Martesia striata ("wood piddocks"), a type of boring bivalve that frequently drills into marine driftwood and other firm or hard substrates.

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