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Archaeognatha (class Insecta, subclass Apterygota) One of the two apterygote orders, comprising fusiform, subcylindrical insects that can run fast and jump by flexion of the abdomen. The body is covered with pigmented scales, and the thorax is strongly arched. Ocelli are present, and the compound eyes are large and contiguous. The mandibles are monocondylar, and the maxillary palps are long and seven-segmented. The abdomen has ventral styles on segments 2–9, used for running on sloping ground, and the posterior portion of the abdomen bears a pair of cerci and a single, much longer, dorsal appendage (the appendix dorsalis). These insects are free-living and nocturnal, feeding on lichen, algae, and vegetable debris. Postembryonic development is slow (six months to two years), and moulting occurs throughout the entire life-span. The 250 or so species are of little economic importance.