Rediscovery of Arthrodamaeus rossicus (Acari: Oribatida: Gymnodamaeidae) with remarks on its generic status and ontogeny of the genus

Abstract

Herein, the first detailed description of adults and juvenile instars of Arthodamaeus rossicus along with detailed illustrations are provided. Taxonomic status and generic placement of this species are discussed, and it is assigned to Arthrodamaeus (comb. nov.). The larva and nymphs are generally similar in their habitus. Basic characteristics in juveniles are the less sclerotized and unpigmented body with granulate surface of gastronotum, larva with 12 pairs of gastronotal setae, nymphs with 10 pairs of gastronotal setae (setae la, lm and d-series absent, but setae lp and p-series present). Larvae have a faint transverse ridge-like structure on prodorsum between interlamellar setae, whereas nymphs have no ridge-like structure on prodorsum, but with large excrescence on posterior end of gastronotum, bearing one pair of long (h1) setae. Conspicuous characters in the larval stage are the long interlamellar setae, which are reduced in nymphs and adults to minute setae, and the various lengths of gastronotal setae. All stages of nymphs carry gastronotic exuviae with reticulate granular sculpture of the previous instars. Adults are coated with thick cerotegument on the idiosoma, legs and most body setae. The sensillus is dilated in its distal part and strongly barbed. The notogaster has three pairs of irregular longitudinal ridge-like structures (procuticle); a pair of subtriangular tubercles Sa; five pairs of notogastral setae and a pair of strongly developed tubercles Sp on epimeral region III. Comparative characteristics of juvenile stages and adults of species belonging to Arthrodamaeus are given based on our own data and available literature sources. Arthodamaeus rossicus is a Western Palaearctic species, currently known from Eastern Europe (European part of Russia), and appears to be primarily an inhabitant of mixed forests. It prefers the soil, mosses on soil and trunks of trees as well as decaying stumps of deciduous trees.