In Parasitiformes, the sternal and genital shields (or regions when shields are poorly sclerotized) primitively contains numerous setae, but these are reduced to just 5 pairs in derived Mesostigmata, sternal setaesternal setae:
in Mesostigmata, the five pairs of setae in the intercoxal region designated st1-5; st1-3 are present in the larva and usually are borne on a sternal shield in the adult female; st4, the metasternal setae, are added in the deutonymph, often are borne on metasternal platelets, and sometimes on the sternal shield; st5, the genital setae, are added in the protonymph and usually borne on or are inserted laterad the epigynal shield in the adult female.
st1–5 (st5 is actually a genital setagenital seta:
a seta on a genital shield or valve; seta st5 in the Mesostigmata; the genitals g1-g2 in spider mites; in the Eriophyoidea, coxisternal seta 3a.
). Acariform mites lack sternal shields and typically have 1, 2 or several pairs of setae in each coxisternal region.
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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