Carapace

Diagram of a prawn, with the carapace highlighted in red.

A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.

Crustaceans

The molted carapace of a lady crab from Long Beach, New York.

In crustaceans, the carapace is a part of the exoskeleton that covers the cephalothorax. The carapace 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.^[1]

Zooplankton within the phylum Crustacea also have a carapace. These include Cladocera, ostracods, and isopods, however isopods only have a developed "cephalic shield" carapace covering the head.

Arachnida

Diagram of an arachnid, with the carapace highlighted in purple

In arachnids, the carapace is formed by the fusion of prosomal tergites into a single plate which carries the eyes, ocularium, ozopores (a pair of openings of the scent gland of Opiliones) and diverse phaneres.^[2]

In a few orders, such as Solifugae and Schizomida, the carapace may be subdivided. In Opiliones, some authors prefer to use the term carapace interchangeably with the term cephalothorax, which is incorrect usage, because carapace refers only to the dorsal part of the exoskeleton of the cephalothorax.

Alternative terms for the carapace of arachnids and their relatives, which avoids confusion with crustaceans, are prosomal dorsal shield and peltidium.

Turtles and tortoises

A Greek tortoise shell opened to show the skeleton from below

The carapace is the dorsal (back) convex part of the shell structure of a turtle, consisting primarily of the animal's ribcage, dermal armor and scutes.^[3][4]

References

1. Dean Pentcheff (ed.). "Carapace". Crustacea Glossary. Natural History Museum of Los Angeles County. Retrieved 17 June 2012.
2. Jan Beccaloni (2009). Arachnids. University of California Press. ISBN 978-0-520-26140-2.
3. A. S. Romer (1956). Osteology of the Reptiles. University of Chicago Press.
4. R. Zangerl (1969). "The turtle shell". In C. Gans, D. d'A. Bellairs & T. A. Parsons. Biology of the Reptilia 1. London: Academic Press. pp. 311–340.