Morphology of juvenile instars of Furcoribula furcillata and Zygoribatula exilis (Acari, Oribatida)

Abstract

The morphology of juvenile instars of the oribatid mites Furcoribula furcillata (Nordenskild, 1901) (Astegistidae) and Zygoribatula exilis (Nicolet, 1855) (Oribatulidae) is described and illustrated. All instars are from moss on trees (Quercur robur). Those of F. furcillata are the first to be described for Astegistidae, and are characterized by the following traits: body cuticle smooth; rostrum rounded except for medial mucro; prodorsal setae setiform; dorsal gastronotic region with pigmented, well-bordered sclerite; larva with 12 pairs and nymphs with 15 pairs of setiform gastronotic setae; larva with two pairs of paraproctal setae; tarsi II only with one solenidion. The juvenile instars of Zygoribatula exilis are similar morphologically to those of other species of Zygoribatula, and this genus can be included among those in which species are difficult to distinguish based on juvenile characteristics alone.