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Cheliceral segmentation

The maximum number of cheliceral segments in mites is three: a basal article, a middle article that usually ends in a fixed digit, and a movable digit that opposes the fixed digit.  However, in some uropodid mites, the chelicerae are very elongate and the middle article is subdivided.

Most parasitiform mites have 3-segmented chelicerae, although in ticks and some parasitic Mesostigmata the chelicerae are so modified for blood-feeding that segmentation is obscured.

Most acariform mites have lost the basal segment and the chelicerae appear to be 2-segmented, although the regression or loss of the fixed digit may obscure this and in spider mites and their relatives the chelicerae are so modified for feeding on plant cells that segmentation is obscured.  In heterostigmatine Prostigmata, the chelicerae are hidden within a gnathosomal capsule, but in the hypopal stage of Astigmatina the chelicerae are truly absent.