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one of numerous movable hairlike pectinate or hooked protuberances of the cuticle in invertebrates. Chaetae have many purposes. In some invertebrates they help support the body during digging (Echiuroidae, many annelid worms, Pogonophora) or crawling (annelid worms). In other invertebrates it serves a protective function (certain polychaetes and brachiopods), and in still others it is used in capturing prey (chaetognaths). In polychaetes, the chaetae are part of the primitive extremities—parapodia. Each chaeta consists of a single cell on the floor of a cutaneous invagination. The chaetae of arthropods are hairlike or feathery protuberances of the chitinous cuticle; they are sense organs (mainly of touch) and sometimes help protect the body, especially the wings, from excessive wetness. Some ticks and mites still preserve primitive metamerism in the arrangement of their chaetae.