Morphology, distribution and certain population parameters of the Arctic mite Oribatella arctica (Acari: Oribatida: Oribatellidae)

Abstract

In this study, the morphology, distribution, ecology, stage structure and sex ratio of the Arctic oribatid mite Oribatella arctica (Thor, 1930) were investigated. The juveniles of this species are similar to those of other species of Oribatella Banks, 1895, possessing mostly long and barbed prodorsal setae, long and barbed gastronotal setae in the larva and long, barbed peripheral gastronotal setae in the nymphs. The larva of O. arctica differs from that of most other Oribatella species principally by the shape of the sensillus and the length of seta le. Nymphs differ chiefly by the number and shape of some central setae (c1 and d-series) on the gastronotum and the attachment of the exuvial scalps of previous instars to the gastronotum. All nymphs of O. arctica have central setae c1, da and dm short and smooth, whereas the presence and shape of seta dp varies between nymphal stages (it can be long and barbed, short and smooth, alveolar or absent). Oribatella arctica nymphs rarely carry the exuvial scalps on the gastronotum, but if so, these scalps are fastened to the gastronotum, using setae c1, c2 and of l-series, whereas most of other species of Oribatella carry the exuvial scalps, using special muffs that are formed while moulting on the apical parts of setal pair da. The adult of O. arctica appears initially similar to other species of Oribatella, but differs mainly in the shape of the lamella and lamellar cusps, presence of translamella, shape of the sensillus, length of most notogastral setae, location of setae lp, h2 and h3, body size, number of claws on legs, and shape of epimeral seta 4c.