Variability of external morphology of Eueremaeus Mihelčič, 1963 (Acari, Oribatida, Eremaeidae) in the light of ontogeny of four species

Abstract

In this study the variability of the external morphology of Eueremaeus Mihelčič, 1963 was investigated, in the light of the ontogeny of Eueremaeus oblongus (C.L. Koch, 1835), Eueremaeus intermedius Mihelčič, 1963, Eueremaeus silvestris Forsslund, 1956 and Eueremaeus travei Mihelčič, 1963 and the literature. Morphological variability occurs in all species and includes mainly the presence and size of foveae in different parts of body of the juveniles, shape of femora I–IV of nymphs and shape of prodorsal lamellar costulae and tubercles between the bothridia of the adults. Eueremaeus intermedius and Eu. silvestris are considered by some authors as synonyms of Eu. oblongus, but in the light of our observations these species differ by the morphology of the juveniles and adults from Eu. oblongus, so we provisionally reject these synonyms until the type or topotypic material of these species can be compared. All these species are relatively similar in the larva, and differentiation of their morphology increases during ontogeny and is well observed in the tritonymph. The tritonymph of Eu. intermedius has distinctly shorter setae in, h3 and p2 than those of Eu. oblongus and Eu. silvestris, whereas the tritonymph of Eu. silvestris has longer sensillus, with slimmer head than those of Eu. intermedius and Eu. oblongus. The adult of Eu. intermedius has prodorsal lamellar costulae more widely separated than in Eu. oblongus and Eu. silvestris, shorter seta in and larger subtriangular post-anal process than in these species, whereas the adult of Eu. silvestris has longer sensillus, with slimmer head than in Eu. intermedius and Eu. oblongus. The latter species has barbed anal setae, whereas other two species have these setae smooth. The nymphs of Eu. travei have stocky femora I–IV, with dorsal serrate keels, whereas in other species these segments are slimmer and without dorsal keels. The adult of Eu. travei is larger, more stocky and has longer prodorsal lamellar costulae than those of other species. We observed in the adult of Eu. oblongus for the first time setae c3 and c1 on the notogaster, which inform about the order of loss of these setae in the Eremaeidae.