; 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.
Subjects: Earth Sciences and Geography — Zoology and Animal Sciences.