Gnathosoma
The central part, the subcapitulum (S, = infracapitulum), contains the mouth and the tube through which food passes. Its skeleton is formed from the enlargement and fusion of the walls of the basal segments (coxae) of the appendages (pedipalps, usually abbreviated to palps, pa) which flank it. The anterior part of the subcapitulum is called the hypostome (h) and the basal part the basis capituli (bcap, = basis gnathosomatica, gnathosomatic base). The mite subcapitulum is roughly triangular in shape, but its precise form is very variable. In most oribatids, a pair of anteroventral subcapitular setae are massively expanded into toothed structures (r, rutella; sing. rutellum), while free¬-living and ectoparasitic
Mesostigmata have a forked tritosternum (tst), originating from the idiosoma, lying over the midline ventrally. The tick hypostome is a characteristic finger-like structure, which has rows of backwardly curved teeth on its ventral surface. The basis capituli of the Ixodidae may have dorsal (upper surface) and ventral projections called, respectively, cornua (cor) and auriculae (au). Females also have a pair of dorsal depressions (po, porose areas).
One palp is situated on either side of the subcapitulum and comprises a maximum of six free segments (= articles, palpomeres) named, from base to tip, the trochanter (Tr), femur (Fe), genu (Ge), tibia (Ti), tarsus (Ta) and apotele (apo). The basic palpal form is much modified to cope with the handling and sampling of different food types. Fusion of segments, particularly of the femur and genu and the tibia and tarsus, and variation in size and shape all occur. The tarsus usually bears a terminal cluster of chemosensory setae. Only Mesostigmata have a full complement of palpal segments, although the apotele is reduced to a membranous two- or three-pronged structure located basally on the inner face