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Cirripedia

Cirripedia (cirripedes; barnacles; phylum Arthropoda, subphylum Crustacea) Class of crustaceans comprising the familiar barnacles that settle on rocks, submerged timbers, corals, shells and the undersides of ships. They are entirely marine. The name literally means ‘comb-foot’. After a free-swimming larval stage the bivalved cypris larva attaches itself to the substratum by means of cement secreted from glands in the first antennae. The body rotates and the thoracic appendages (usually six) are modified to form cirri (flexible feeding appendages) that point upwards or sideways through the gape in the carapace. The carapace persists in the adult barnacle as an inner mantle which is covered externally by calcareous plates. In the sessile (unstalked) barnacles (e.g. Balanus), the plates are large and heavy, making the organism very well adapted to the high-energy conditions of a rocky, intertidal zone. Two orders of cirripedes have fossil records: the Thoracica and Acrothoracica. The Thoracica includes stalked forms (e.g. the modern Lepas or goose barnacle) and unstalked forms (e.g. Balanus). The stalked form is thought to be the more primitive. The ancestral form of the cirripedes probably resembled the cypris larva. The undoubted fossil record of the Thoracica began in the Upper Silurian with Cyprolepis (a stalked form), but fragments and disarticulated plates of Cambrian- Ordovician age have also been assigned to this group. The Acrothoracica are the smallest cirripedes. They bore into calcareous material such as shells and corals. Their distinctive burrows have been recorded as trace fossils from Devonian rocks.

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Cirripedia

Cirripedia (barnacles; phylum Arthropoda, subphylum Crustacea) The only class of crustaceans, apart from parasitic groups, in which the adults are wholly sessile. Cirripedes are the familiar barnacles that settle on rocks, submerged timbers, corals, shells, and the undersides of ships. The 900 or so described species are entirely marine. Cirripedes have free-swimming larvae, the last of which is called a cypris larva. The larval carapace persists and in adult barnacles is often termed the mantle. In the common barnacles (Thoracica) calcareous plates develop and cover the mantle externally, and there are both stalked and sessile groups. Except for the cement glands, the first antennae are vestigial, and the second antennae are present only in the larvae. Typically, there are six pairs of long, biramous, thoracic feeding appendages (cirri) which are projected through the mantle opening to scoop up plankton. The body comprises a cephalic region and an anterior trunk (or thoracic region), with very little indication of external segmentation. Apart from the typical ‘barnacle’ type, there are forms (order Acrothoracica) modified for boring into shells and corals, and naked forms (orders Ascothoracica and Rhizocephala) which parasitize other marine organisms.

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barnacles

barnacles
1. See CIRRIPEDIA; CRUSTACEA; THORACICA

2. (acorn barnacles) See BALANIDAE.

3. (goose barnacles) See LEPADIDAE.

4. (parasitic barnacles) See RHIZOCEPHALA.

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barnacles

barnacles See BALANIDAE; and CIRRIPEDIA.

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