Xenillus baderi, Mahunka, S., 1996

Mahunka, S., 1996, Oribatids from Switzerland II. (Acari: Oribatida). (Acarologica Genavensia XC), Folia Entomologica Hungarica 57, pp. 125-129 : 126-128

Xenillus baderi sp. n.

(Figs 1-4)

Measurements - Length of body: 1042-1181 µm, width of body: 722-793 µm.

Integument: Whole body covered by thick cerotegument layer, the cuticle with irregular foveolae.

Prodorsum: Rostrum waved, concave medially. Lamellae very wide, their large cusps completely covering the rostral part of prodorsum. A well developed median triangle present between the lamellar cusps. Rostral, lamellar and interlamellar setae strong, distinctly aciculate. Rostral setae nearly half as long as lamellar one. Sensillus gradually dilate, its head slightly clavate, finely spiculate. Bothridium long, with some sharp lines in the inner surface.

Notogaster: Whole surface ornamented by characteristic foveolae, their size and distance varying. Dorsosejugal suture convex medially. Notogastral setae - excepting the antero-marginal (c1-c2) and postero-marginal (p1-p3) ones - long, nearly setiform, spiculate, with an aciculate needle-shaped distal end. The other setae much shorter, blunt at tip and also roughened or distinctly spiculate. Five pairs of lyrifissures present.

Lateral part of podosoma: The embedded specimens were unsuitable to study this features.

Ventral regions: Mentum and the coxisternal region ornamented by distinct, sometimes fused foveolae. This sculpture consists of larger foveolae on the ventral plates. Epimeral borders only partly visible, apodemes and borders 2 and sejugal ones well observable, long, the latter fused medially. Epimeral setal formula: 3-1-3-3. All setae erect, short, blunt at tip and finely barbed. Genital plates darker than the rest of this region. Five pairs of genital setae also blunt at tip, they are longer than the epimeral ones. Anal and adanal setae similar to notgastral ones, mostly bacilliform.

Legs: All legs tridactylous, a weak heterodactyly present. All femora have distinct, ventral blades. Trochanters III and IV with a strong ventro-distal spur each. Setal formulae of legs typical for this genus. Solenidium phi1 of leg I arising on a large tubercle, phi2 located behind it. Seta l' strong and long, seta v" of tarsus IV short spiniform.

Material examined: Holotype: Switzerland, Tessin, Verzascatal, "Frasco" , X. 1947. Leg. E. Wettstein ( W 1024 ). 1 paratype: Switzerland, "Faletsche" , 18. XI 1943. Leg. E. Wettstein ( W 1026 ). 1 paratype: Switzerland, "Aunenona Siders" . IV. 1943. Leg. E. Wettstein ( W 1023 ).

The holotype and 1 paratype are deposited in the Museum of Natural History of Basle, 1 paratype ( W 1023 ) deposited in the Hungarian Natural History Museum, Budapest, with an identification number ( PO-1570-96 ) of the specimens in the Collection of Arachnida.

Remarks: In spite of the fact that many authors (e.g. Woolley 1966) have already discussed the genus Xenillus Robineau-Desvoidy, 1839 a part of the species is still unclear.

Figs 1-4. Xenillus baderi sp. n. - 1: body in dorsal view, 2: rostrum, 3: sensillus and humeral region, 4: sculpture of the notogaster

It seems almost certain that the various authors using a species name, in fact, meant different species. Furthermore, it is more than certain that far more species live in the Palaearctic region than the number known today. This confusion is also applicable to the species X. clypeator Robineau-Desvoidy , 1839 and X. discrepans Grandjean , 1936. Two subspecies of the latter were described by Pérez-Inigo in 1976 and 1984. Without thorough study of the types these problems cannot be solved. The new species unequivocally belong to the species-group of Pérez-Inigo's X. discrepans , though I regard the type of the group to be X. clypeator . It is beyond doubt that the presently studied taxon comes quite close to the form of X. discrepans sensu Moraza, Herrera and Pérez-Inigo 1980.

According to my opinion on the basis of the form of the lamellae the new species belongs to the " clypeator "-species group. It is well characterised by the unique form of the notogastral setae and by notogastral sculpture. The length of the interlamellar setae distinguish the new species from all related species.

Etymology: I dedicate the new species to Dr. C. Bader, one of the greatest hydracarologist, and we also thank his valuable help during in our studies in Basel on the Swiss oribatids.