Genital Shield Form in Adult Female

Genital shields are sclerotized plates that protect the genital opening/ ovipore on the venter of mites.  Although called genital shields (also epigynial shields), in many mite lineage insemination occurs via a secondary system that is no longer associated with the ovipore and the true genital opening in the adult female is removed from the ovipore.  Nevertheless, the form of the so-called genital shield in the female is often diagnostic for major mite groups.

In the Mesostigmata, the genital opening is transverse and protected by 1-4 separate sclerites.  The median, and usually largest or only, sclerite is hinged posteriorly and opens like an anteriorly directed trap door.  In the Monogynaspida and Sejida there is only a single median genital (or 'epigynial') monogynaspid shield, but in the Trigynaspida there are usually 2-3 distinct shields (trigynaspid condition), and sometimes 4 shields (i.e. quadrigynaspid - also found in Holothyrida). One family of Monogynaspida (Parasitidae) have large secondary sternal sclerites that flank an anteriorly acuminate monogynaspid genital shield, a condition called parasitoid that could be confused with the trigynaspid condition.  In some monogynaspids, an opisthogenital shield is present, i.e. the genital shield is fused to a ventral shield bearing one or more pairs of setae.  Most Mesostigmata feed only on fluids (usually externally digested prey) and have a fairly small anal opening covered by a pair of small sclerites and well removed from the genital opening.

In Sarcoptiformes, the genital and anal openings both tend to be large (most sarcoptiform mites ingest solid food).  If they have separate adgenital and adanal plates lateral to the genital and anal shields, respectively, the condition is called macropyline.  The typical macropyline complex of shields covers most of the post-coxal venter of the mite.  Both genital and anal shields meet along the midline and sometimes the genital shields are divided transversely to form four shields.  In derived oribatid mites the genital and anal plates are surrounded by a large ventral shield composed of aggenital and adanal elements, a condition called brachypyline.  Although traditionally used only for oribatid mites, the brachypyline condition is also found in many other acariform mites with longitudinally divided genital and anal shields.

In addition to the above general conditions, other forms of genital opening are distinctive.  In the Astigmatina, the female's genital shields often converge anteriorly in an inverted-V form.  In spider mites, sclerotized genital shields are absent and the large and transverse genital opening is surrounded by wrinkled, soft plicate cuticle.  In other Prostigmata, the genital and anal plates are coalesced into a single unit.