Arrhopalites brevicornis

Description. Female. Body (head + trunk) length of type series (females, N = 4) ranging between 0.71 and 0.81 mm, average 0.74 mm, holotype with 0.75 mm. Habitus as in Fig. 1. Specimens pale yellowish with brownish spots of pigment on frontal and dorsal head and dorso-lateral large abdomen. Body chaetae smooth and acuminate, with the exception of the subanal appendage. Head (Figs 1, 2). Antennae shorter than the body, with 0.32 mm in the holotype (Fig. 1), ratio antennae: head length of the holotype 1.3: 1, type series average 1.4: 1. Holotype antennal segments ratio of Ant I: II: III: IV as 1: 1.6: 2.3: 4.3, and of type series (N = 4) as 1: 1.3 - 2.7: 2.1 - 3.3: 3.8 - 6.7. Ant IV short and stout, about twice or less the size of Ant III (in holotype, ratio Ant III: IV = 1: 1.87), without subsegments, with about 87 regular chaetae of different sizes distributed in apparently 13 whorls (Fig. 2 A). Ant III slightly swollen with 17 chaetae, Ape, Ae, Ap, Ai, Aa, Api, and Aai present, Api slightly reduced, Aai as the accessory microsensillum, sense rods not swollen inside separate invaginations (Fig. 2 B). Ant II with 13 regular chaetae, Ant I with 7, the two more apical reduced (Fig. 2 C). Eyes 1 + 1, head length (eyes to mouth) of holotype 0.25 mm. Clypeal area a-f lines with 7 (+ 1) / 7 / 5 / 4 - 5 / 5 / 6 chaetae respectively, plus 3 central chaetae of unclear homologies; interantennal area α and β lines with 2 / 1 (+ 1) short chaetae respectively, plus 2 + 2 small oval organs (pseudopores) and 1 + 1 large circles lacking tegument granules near the lateral chaetae on α line; frontal area A-C lines with 1 / 1 / 2 (+ 1) short stout spines, D line with 2 elongate thinner erect chaetae (Fig. 2 D). Ventral groove with 2 surrounding chaetae from lines a and b, labial basomedian field with 4, basolateral field with 5 chaetae (Fig. 2 E). Labial papilla E lateral finger-shaped, not reaching the papilla apex, other labial structures unclear. Maxillary outer lobe apical chaeta longer than the basal one, sublobal plate with three sublobal hairs (Fig. 2 F). Distal margin of the clypeus with 3 prelabral chaetae, labral chaetotaxy with 2 (+ 1) p, 2 (+ 1) m and 2 a chaetae, all subequal (Fig. 2 G). Trunk (Fig. 3 A, B). Trunk length of holotype 0.5 mm. Large abdomen: thorax continuous with abdomen, without any constrictions. Th II with 1 a and 3 m chaetae; Th III with 1 a and 3 m chaetae; Abd I with 5 a, 4 m and 1 p chaetae, respectively. Three chaetae (1 - 3) on the upper side of bothriotrichum A, plus accessory a 1 nearby its alveolus; b 1 accessory chaeta between B and C bothriotricha, c 2 just under C, c 1 absent; bothriotricha A-C misaligned, with B bothriotrichum closer to C than A; dorso-posterior longitudinal series dI- 1, dII- 1, dIII- 1 with 5 - 7, 9 - 10 and 6 - 8 chaetae, respectively; two rows with 3 chaetae each between C and D bothriotricha; D with 4 surrounding chaetae posteriorly; parafurcal area (furcula basis) with 8 regular chaetae; ventral complex with 1 chaeta (Fig. 3 A). Small abdomen of the female: dorsal anal valve with as 2 - 4, ms 1 - 5?, mps 1 - 3, and ps 1 - 2 chaetae, ms 1 and mps 1 - 3 sword-shaped and smooth, 2 cuticular spines surrounding mps 2; ventral anal valves each with ai 1 - 6, ami 1 - 2, mi 1 - 5, mpi 1 - 2, and pi 1 - 3 chaetae, mi 3 and mpi 1 - 2 sword-shaped and smooth, mi 5 as the subanal appendage long (similar in length to mi 3, mpi 1 - 2) with a spatulated and apically serrated apex (sometimes one of the lateral edges is also distally serrated), curved toward the genital opening, 2 cuticular spines surrounding mpi 2 (Fig. 3 B). Genital plate of the female unclear. Abdominal appendages (Fig. 3 C-F) Collophore with 1 distal chaeta on each side, with a pair of a little wrinkled, almost smooth, sacs. Tenaculum with 3 teeth on each ramus plus the basal tubercle, with a single unpaired apical chaeta. Furcal size length in holotype: manubrium = 75 µm; dens = 113 µm; and mucro = 75 µm (ratio 1: 1.5: 1). Manubrium with 5 dorsal chaetae on each side, the most proximal thinner than the others (Fig. 3 C); dens ventral (or anterior) formula from the apex to the basis as 3,2,1,1,1, all chaetae enlarged except for the most proximal one, (Fig. 3 D); dens dorsally (or posteriorly) with 16 chaetae, 7 of them on the lateral edges of the more distal region more robust, almost spine-like (Fig. 3 E). Mucro apically swollen with both edges serrated from the basis until almost the apex (Fig. 3 F). Legs. (Figs 3 A, 4) Epicoxae, subcoxae and coxae I-III with 1,0,1 / 1,1,4 / 1,1,4 chaetae, respectively, coxae II-III with 1 long and 1 tiny chaeta each (Fig. 3 A). Trochanters I-III with 4 chaetae each, II-III with 1 chaeta each modified as an anterior trochanteral organ (Fig. 4 A-C). Femurs I-III with 13 / 13 / 14 chaetae respectively, of which 1 / 1 / 3 as reduced chaetae (Fig. 4 A-C). Tibiotarsi without oval organs, tibiotarsus I region F with 3 chaetae (FPae, FPe, and FPpe), whorls I-V with 9,8,8,8,9 chaetae respectively, whorl I without clearly modified chaetae except for a larger dorsal one, whorl V with 2 ventro-distal chaetae (Fig. 4 D). Tibiotarsus II region F with 3 chaetae (FPae, FPe, and FPpe), whorls I-V with 9,8,8,8,7 chaetae respectively, whorl I without clearly modified chaetae except for a slightly larger dorsal one, whorl V with 1 ventro-distal chaeta (Fig. 4 E). Tibiotarsus III region F with 4 chaetae (FPae, FPe, FPpe, and FSa), whorls I-V with 9,8,8,8,7 chaetae respectively, whorl I without clearly modified chaetae except for a slightly larger dorsal one, whorl V with 1 ventro-distal chaeta (Fig. 4 F). Foot complexes I-III with 2 pretarsal chaetae each, 1 anterior and 1 posterior; ungues (claws) without cavity or pseudonychia, but with an underdeveloped tunica covering about 2 / 3 up to 3 / 4 of the dorsal ungues, lateral lamellae apparently lacking teeth, each unguis with one internal tooth; unguis I slender, III broad (Fig. 4 D-F). Unguiculi (empodia) never surpassing the ungues, unguiculus I almost reaching the apex of unguis I, unguiculi II-III clearly shorter; unguiculi I-II with one proximal internal tooth each, unguiculus III with 2 more distal teeth (Fig. 4 D-F). Male. Not found, species possibly parthenogenetic.

Figs 1, 2, 3, 4

Diagnosis. Female. Antennae short, about 1.4 times the head length. Ant IV not subdivided and short, about twice or less the length of Ant III. Eyes 1 + 1. Clypeal area a-f lines with 7 (+ 1) / 7 / 5 / 4 - 5 / 5 / 6 chaetae respectively, plus 3 central chaetae with unclear homologies, frontal area A-C lines with 1 / 1 / 2 (+ 1) short stout spines. Small abdomen, dorsal anal valve with 2 cuticular spines per side and 4 sword-shaped smooth chaetae (ms 1, mps 1 - 3), ventral anal valves with 2 cuticular spines each and 3 sword-shaped smooth chaetae (mi 3, mpi 1 - 2), subanal appendage long, similar in length to mi 3, mpi 1 - 2, with a spatulated and apically serrated apex. Manubrium with 5 chaetae on each side, dens ventral formula from the apex to the basis as 3,2,1,1,1, dorsally with 16 chaetae. Mucro with both edges serrated, apically swollen. Ungues I slender, III broad, all with an underdeveloped tunica, unguiculus III with 2 inner teeth.

Distribution and habitat. The new species was collected and only recorded in Jilin Province, Changling County, at the Ecological Research Station for Grassland Farm (ERSGF). This region is characterized by a semi-arid continental monsoon climate, with cold, dry winters and warm, rainy summers. Annual mean temperature in the region ranges from 4.68 to 6.48 ° C, and annual precipitation is 280 to 400 mm with about 70 % falling in the June-August period (Changling County Climate Station, Jilin Province). Changling County is located at a transitional zone of cropping and grazing, with high economical potential. However, drastic environmental disturbances are happening in this region, like sand and dust storms, emergence of saline-alkali soils, and land over-utilization.

Etymology. The new species was named after its short antenna (from Latin brevi - = short; cornis = " horns ", antennae).