carapace

carapace, shield, or shell covering, found over all or part of the anterior dorsal portion of an animal. In lobsters, shrimps, crayfish, and crabs, the carapace is the part of the exoskeleton that covers the head and thorax and protects the dorsal and lateral surfaces. In many crustaceans, the term carapace is also used to describe the hard, protective covering of the cephalothorax, as that of the horseshoe crab. The carapace of a turtle's shell is composed of expanded ribs and vertebrae overlain by dermal plates and horny scales.

A carapace is a dorsal section of an exoskeleton or shell in a number of animal groups.

Crustaceans

In crustaceans, the carapace is a part of the exoskeleton that covers the cephalothorax. It is particularly well developed in lobsters and crabs. It functions as a protective cover over the cephalothorax. Where it projects forward beyond the eyes, this projection is called a rostrum. The carapace is calcified to varying degrees in different crustaceans. Zooplankton within the phylum Crustacea also have a carapace. These include Cladocera, Copepods, Ostracods, Amphipods, and Isopods.

Arachnida

In arachnids, the carapace is formed by the fusion of prosomal (= of cephalothorax) tergites into a single plate which carries the eyes, ocularium, ozopores (a pair of openings of the scent gland of Opiliones) and diverse phaneres. In a few orders, such as Solifugae and Schizomida it may be subdivided. In Opiliones some authors prefer to use the term carapace interchangeably with cephalothorax, which is incorrect, because carapace refers only to the dorsal part of it. An alternative term for the carapace of arachnids and their relatives, which avoids confusion with crustaceans, is prosomal dorsal shield.

Turtles and tortoises

The carapace is the dorsal, convex part of the shell structure of a turtle, consisting primarily of the animal's broad ribcage. The spine and ribs are fused to bony plates beneath the skin which interlock to form a hard shell. Exterior to the skin the shell is covered by scutes, horny plates which protect the shell from scrapes and bruises. Turtles can survive surprisingly severe injuries to the carapace, and even deep cracks or missing portions can fill in with bone and heal. The softshell turtles, pig-nose turtle and leatherback sea turtle lack scutes and the bony carapace is covered only by skin. The carapaces of many species of turtles are brightly colored and patterned and allow individuals to identify others of their species at a distance. The carapaces expand and grow outward like growth rings on a tree as the turtle or tortoise matures. The consistency of the carapace resembles hard keratin rather than bone. The plastron makes up the lower half of a turtle's shell.