Differentiation of external morphology of Oribatella Banks, 1895 (Acari: Oribatida: Oribatellidae), in light of the ontogeny of three species

Abstract

Differentiation of external morphology of Oribatella Banks, 1895 was investigated, in light of the ontogeny of O. quadricornuta (Michael, 1880), O. superbula (Berlese,1904) and O. calcarata (CL Koch, 1835) studied here for the first time, and that of the other species from the literature. The pattern of gastronotal setae in larvae is similar, except for lack of seta h 3 in O. nortoni Behan-Pelletier, 2011, while that of nymphs and adults is differentiated. The nymphs of most species have 15 pairs of gastronotal setae, but those of O. metzi Behan-Pelletier, 2011 and most nymphs of O. calcarata have 13 pairs. The nymphs of most species carry the exuvial scalps of previous instars on apical parts of gastronotal setae da, while setae dm and dp, located under these scalps, are subjected to translocation, reduction in size or loss. In O. berlesei (Michael, 1898), O. nortoni, O. quadricornuta and O. sexdentata Berlese, 1916 pair dp takes a more lateral position, compared with the larvae, in O. superbula and O. canadensis Behan-Pelletier and Eamer, 2010 it is reduced in size (in the latter species pair dm is also reduced), while O. metzi loses setae dm and dp. In contrast, the nymphs of O. calcarata do not carry the scalps, and usually lose setae c 1 and dm. The adults of all species lose setae c 1, c 3 and d-series, compared with the tritonymph, and only 10 pairs of notogastral setae remain (c 2, l-, h- and p-series), but O. quadricornuta and O. calcarata rarely retain seta c 3 unilaterally, which indicates the order of setal loss in Oribatella according to Shaldybina (1972).