Sinella gracilis sp. nov.

Figs 5, 59−69

Types. Holotype: female on slide, China: Neimenggu: Kalaqin Qi: Longshan town, 42°0.561’N, 118°45.499’E, 3.viii.2012, Z. Chen leg. (sample number NM08031). Paratypes: 3 females on slide and 1 in alcohol, same data as holotype.

Description. Body length up to 0.98 mm. Body yellow white often with weak orange pigment (Fig. 5).

Antenna 1.5 times as long as cephalic diagonal. Antennal segments ratio as I: II: III: IV = 1: 2.1: 1.5: 2.86– 3. 8. Long smooth straight chaetae absent. Two internal S of Ant.III organ not clearly seen.

Omma 1+1. Lateral process of labial palp thick as normal chaetae. Labial chaeta R ciliate and others smooth, R/M=0.7; chaetae G1–3 smooth and others posterior to labium ciliate; chaetae X, X2 and X4 ciliate. Cephalic groove with 8(7) chaetae, all ciliate except G1 (Fig. 59). Dorsal cephalic chaetotaxy with 3 median (M) mac. Clypeal chaetae 7, all ciliate (Fig. 60).

Trochanteral organ with 10–13 smooth, thin, spiny chaetae; 8–11 in arms and 2 between them (Fig. 61). Inner differentiated tibiotarsal chaetae ciliate with ciliations not closely appressed to axis. Most distal whorl with 10 ciliate chaetae. Unguiculus outer edge with a large tooth. Tenent hairs clavate, subequal to unguiculus in length (Fig. 62). Abd.IV 2.1 times as Abd.III in length along dorsal midline. Ventral tube anteriorly with 5+5 ciliate chaetae, two of them much larger (Fig. 63); posteriorly with 6 smooth chaetae (Fig. 64); each lateral flap with 5 smooth and 1 ciliate chaetae. Manubrium without smooth straight chaetae, most distal part with 5+5 anterior and 4+4 posterior ciliate chaetae in a row. Manubrial plaque with 2 pseudopores and 2 ciliate chaetae. Distal smooth part of dens 2.0 times of mucro in length. Mucro bidentate with two teeth subequal; basal spine short with tip reaching the subapical tooth (Fig. 65).

Th.II with 3 medio-medial (m1, m2, m 2i), 3 medio-lateral (m4, m 4i, m4p) and 19–20 posterior mac; p5 and p6 as mic. Th.III with 23 mac; p5 and p6 as mic (Fig. 66). Abd.I with 6(7) (a2, a3, m2–4, m 2i, m4p) mac; a2 rarely as mac. Abd.II with 5 (a2, a3, m3, m3e, m3ep) central and 1 (m5) lateral mac. Abd.III with 2 (a2, m3) central and 2 (pm6, p6) lateral mac; ms absent (Fig. 69). Abd.IV with 4 central (M, A4, B5, B6) and 4 lateral mac (E2–4, D3) (Fig. 67). Abd.V with 3 s-chaetae (Fig. 68).

Ecology. Under stones and leaves.

Etymology. Named after the thin spiny chaetae on trochanteral organ.

Remarks. This new species is characterized by very thin, spiny chaetae on trochanteral organ, chaetotaxy of ventral head, lateral mac on Th.II (p5 and p6 as mic, mac m 5i and a 6i absent), 5+5 central mac on Abd.II, and 2+2 central mac on Abd.III. It is similar to S. pauciseta Qu, Zhang & Chen, 2010 but differs from the latter in ciliate labial chaeta R, chaetotaxy of Abd.II–IV, and ventral tube.