2. (Arthropoda: Chelicerata) a. In Acari, the more or less fused dorsal sclerites of the cephalothorax covering the idiosoma of mites and ticks. b. In Arachnida, the upper covering of the cephalothorax.
3. (Arthropoda: Crustacea) a. A cuticular, usually calcified, structure formed by the posterior and lateral extension of the dorsal sclerites of the head of many decapods and other crustaceans, often covering head and thorax. b. In bivalves, a fold of integument extending from the maxillary segment forming the shell. c. In some Cirripedia, the mantle usually with calcified plates.