Like other arthropods, the body and appendages of mites and ticks are enclosed in an external skeleton.
The body, idiosoma (I), is typically oval and without the distinct subdivisions seen in most of the arachnid orders.
The mouthparts (gnathosoma, g, = capitulum) form a discrete structure at the anterior end of the idiosoma, usually slightly ventrally (most/many mites; argasid, or soft, ticks) or sometimes terminally (a few mite families; ixodid, or hard, ticks, larval soft ticks?all). The gnathosoma is delimited from, and articulates with, the idiosoma by the circumcapitular furrow (cf, = circumcapitular suture).
The four pairs of legs originate from the ventral (lower) idiosomal surface, along approximately its anterior half, and are notated from anterior to posterior I, II, III, IV (larvae lack leg IV).
Setae are hair-like extensions of the cuticle occur on the gnathosoma, idiosoma and legs. Different types are sensitive to touch, vibrations or chemicals.
As the chitinous exoskeleton hardens with age, it gradually turns brown (sclerotization). Localized areas of heavier sclerotization (shields, = plates) occur on the idiosoma.In weakly sclerotized mites, the shields can sometimes only be detected because they lack the striations fine folds of the surrounding area.
The number, arrangement and shape of shields and setae are used to distinguish between different groups of Acari and between different life stages.
Discover more about the mouthparts of ticks and mites
Get more information about the suborder Cercomegistina.