Division of Dorsal Shield

In acariform mites, a putative remnant of the chelicerate prosoma is often defined by a dorso-sejugal suture that separates the posterior notogaster from an anterior prodorsum.  This division is visible in most sclerotized acariform mites, especially in the traditional oribatid mites, Astigmatina hypopi, and also in some Prostigmata and Astigmatina adults.

In contrast, the dorso-sejugal plane is not visible in parasitiform mites, and the idiosoma is completely covered by a single holodorsal shield in Holothyrida and many Mesostigmata.  This is also true in some armored Prostigmata (e.g. Labidostommatides) and the dorso-sejugal suture may be obscured in many derived Brachypylina.  The holodorsal shield is often divided in the Mesostigmata, but the division is posterior to the legs, and no dorso-sejugal suture is present.

Multiple dorsal shields are present in many mites, as are reductions of shielding to a single anterior plate or completely soft cuticle.