Differentiation of external morphology of Zetomimidae (Acari: Oribatida) in light of the ontogeny of two species

The morphology of juvenile stages and ontogeny of Heterozetes palustris (Willmann, 1917) and Zetomimus furcatus (Pearce & Warburton, 1906) are redescribed and illustrated. The juveniles of the former species have most prodorsal and gastronotal setae long, and smooth integument with microtuberculate cerotegument, while those of the latter species have most prodorsal and gastronotal setae short, with three pairs of longer and thicker setae in the posterior part of gastronotum, tuberculate integument, and two darker stripes, transverse and longitudinal, in the shape of letter T, with microtuberculate cerotegument. Most of nymphs of Z. furcatus bear one scalp, and rarely 2-3 scalps of previous instars that adhere to the gastronotum, which is observed here for the first time. The adults of both species have several morphological characters of Ceratozetoidea, while their juveniles lack a humeral organ and distinct sclerites, which occur in most Ceratozetoidea.