Ontogenetic instars of the oribatid mite Scheloribates arsizonensis n. sp. (Acari, Oribatida, Scheloribatidae) from Ethiopia

A new species of the genus Scheloribates (Oribatida, Scheloribatidae)— S. (Scheloribates) arsizonensis n. sp. — is described from Ethiopia, based on adult and juvenile instars, collected from litter and green moss in Arsi Mountains National Park. Adults of the new species differ from S. praestantissimus praestantissimus (Berlese, 1916) in having fusiform, distally pointed bothridial seta, the absence of prolamella, and the presence of well-developed notogastral setae p1. The comparison of juveniles of the new species with juveniles of other Scheloribates species is presented. Juveniles of the new species can be distinguished from the other known juveniles of S. (Scheloribates) by the presence of two strong, long, longitudinal, dorsolateral folds on the gastronotum in all instars, long gastronotic seta c3, which is distinctly longer than other gastronotic setae in nymphal instars, the presence of vestigial gastronotic seta h3 in larva, and in the absence of aggenital setae in deutonymph.

In the course of taxonomic identification of materials collected from litter and green moss in Arsi Mountains National Park, Ethiopia (Fig. 1), we found a new species of Scheloribates (from nominate subgenus).The main goal of the paper is to describe and illustrate this new species based on adult and juvenile instars, and compare its juveniles with those of other Scheloribates species.

Methods
Sampling -Substrate samples (litter and mosses) containing oribatid mites were collected using a stainless-steel frame (50 × 50 cm) with a sieve (mesh size 2 × 2 cm).Mites were extracted into 75% ethanol using Berlese's funnels with electric lamps in laboratory conditions (in Institute of Ecology and Evolution, Moscow, Russia).The collection locality is provided in the Material examined section.
Juvenile specimens were associated with adults using criteria outlined by Norton & Ermilov (2014).In particular, they were found in the same samples and had appropriate size and proportions.If more than one similar-sized species was represented in a sample, juveniles were ignored.
Observation and documentation -Specimens were mounted in lactic acid on temporary cavity slides for measurement and illustration.Body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the notogaster (in adult)/gastronotic region (in juveniles).Notogastral/gastronotic width refers to the maximum width of the notogaster in adult (behind pteromorphs) and gastronotic region (in juveniles) in dorsal view.Lengths of body setae were measured in lateral aspect.All body measurements are presented in micrometers.Formulas for leg setation are given in parentheses according to the sequence trochanter-femur-genu-tibia-tarsus (famulus included).Formulas for leg solenidia are given in square brackets according to the sequence genu-tibia-tarsus.Drawings were made with a camera lucida using a Leica transmission light microscope "Leica DM 2500".
In general, juveniles of Scheloribates are similar to each other, however, larva and nymphal instars of S. arsizonensis n. sp.can be distinguished from those of the other above listed species by the: 1) presence of two strong, long, longitudinal, dorsolateral folds on the gastronotum in all instars; 2) long gastronotic seta c 3 which is distinctly longer than other gastronotic setae in nymphal instars; 3) presence of vestige of gastronotic seta h 3 in larva; 4) absence of aggenital setae in deutonymph.

Figure 1
Figure 1 Photographs showing the locus typicus of Scheloribates arsizonensis n. sp. in the Arsi Mountains National Park.