TWO NEW SPECIES OF THE GENUS XENYLLA TULLBERG, 1869 FROM CHINA (COLLEMBOLA: HYPOGASTRURIDAE)

Abstract Two new species of Xenylla from Jilin Province, Northeast China are described and illustrated. Xenylla changlingensis, new species clearly differs from the closely related species X. piceeta Stebaeva & Potapov, 1994 in the presence of dorsal la2 of thoracic segments II and III, the absence of ventral seta p2 on abdominal segment II, 1 median ventral seta above the retinaculum on abdominal segment III, and lack of teeth on the mucro. Xenylla changchunensis, new species is similar to the species X. osetica Stebaeva & Potapov, 1994. However, it is separable from the latter by the presence of a furca, a tenaculum, and the ventral chaetotaxy on abdominal segment III.

The genus Xenylla was established by Tullberg for X. maritima Tullberg, 1869 as type species. It is one of the largest and most widespread genera in the family of Hypogastruridae. According to Thibaud et al. (2004), species in the genus Xenylla are mainly characterized by (1) 5+5, rarely 4+4 ommatidia, (2) postantennal organ absent, (3) mandible short with a well developed molar plate, maxillary head with normal lamellae, (4) furca rarely absent, showing a diverse morphology, if mucro separated from the dens, which normally bears 2 setae; mucro, however, fused with the dens or mucro absent, the dens has 1 or 2 setae, (5) empodium absent, and (6) abdominal segment V tergite with p 3 as sensilla.
So far, about 126 species of the genus Xenylla have been described worldwide (Christiansen 2006). However, only one, X. boerneri Axelson, 1905, has been reported from East China (Zhao et al. 1997). The taxonomy of the fauna of many Chinese habitats is poorly known, especially those of soil. In the present paper, two new species of the genus Xenylla that were found from Northeast China are described. Abbreviations a 1, 2, … -setae 1, 2, … of the anterior row, counted from the "middle line", m 1, 2, … -setae 1, 2, … of the middle row, counted from the "middle line", p 1, 2, … -setae 1, 2, … of the posterior row, counted from the "middle line", c 1, 2, …cervical setae 1, 2, … of area occipitalis, counted from the "middle line", L a 1, 2, …-setae 1, 2, … of the lateral anterior row in thoracic segments, L1, 2, …-lateral setae 1, 2, …. in head (Yosii 1960;Gama 1988 Body length up to 0.95 mm. Body color in alcohol dark blue-violet. With 5+5 ommatidia in head ( Fig. 1). Antennal segment I with 7 setae, antennal segment II with 12 setae. Sensory organ of antennal segment III consists of 2 microsensilla which are embedded in a tegumentary fold and flanked by 2 longer guard sensillum. Antennae IV with a simple apical bulb and 4 weakly thickened sensillum, of which 3 are dorso-external and 1 dorso-internal, and 2 inernal sensillum, which are thinner and shorter than the others (Fig. 8). External maxillary lobe with 2 sublobal hairs.
Tibiotarsi each with 2 capitate, dorsal tenent hairs, which are longer than the inner edge of the claws. Claws with a small, distal internal tooth, 2/ 3 as long as tibiotarsal hairs (Fig. 9). Mucro well separated from the dens with 2 posterior setae, 1/ 2 as long as the dens but dens and mucro particularly slender, width of dens at distal seta about an eighth its length, mucro straight and without teeth (Fig. 10). Ventral tube with 4+4 setae. Retinaculum with 3+3 teeth (Fig. 5). Female genital (Fig. 6) and male genital plate (Fig. 7) normal. Anal spines small, on weakly developed papillae separated at the base, 1/4 as long as claws (Fig. 3).
Chaetotaxy, consisting of short setae and longer and fine sensorial setae. Dorsally head without seta c 2 ( a2 a/c to Babenko), cephalic setae l 1 and l 3 subequal (Fig. 1), thoracic segments II-III with central setae in 3 rows, on thoracic segments II-III p 2 displaced apically relative to p 1, and on thoracic segment III a 2 displaced distally compared with a 1 (Fig. 2), on abdominal segments I-III p 5 present, abdominal segments IV with a 3. Abd. V with a 2 (Fig.3). Ventrally head without seta p 1 (Fig. 4), thoracic segments II and III with a pair of medial setae, abdominal segments II without p 2 and a 5, abdominal segments III with 1 median seta above the retinaculum (Fig. 5).

Comment
The new species is distinguished from all the known species of the genus Xenylla by the ab-sence of mucronal teeth, dorsal side of head without c 2 seta, seta p 2 on tergite of thoracic segments II-III set in front of p 1 seta, head without ventral seta p 1, thoracic segments II and III with a pair of ventral medial setae, abdominal segment II without ventral setae p 2 and a 5, abdominal segment III with 1 median ventral seta above the retinaculum, abdominal segment IV with ventral seta m 1, unguis with 1 internal tooth.

Etymology
This species is named after the type locality.

Taxonomic Remarks
This species keys out to X. piceeta Stebaeva & Potapov, 1994(Babenko et al. 1994, from Far East, southern maritime province, Russia, which was collected in litter of a fir forest (Babenko et al. 1994), but the new species clearly differs from X. piceeta by the presence of dorsal la 2 of thoracic segments II and III, which is stable on the tergites, and the absence of ventral seta p 2 on abdominal segment II. On abdominal segment III, X. changlingensis has only 1 median ventral seta above the retinaculum, while X. piceeta has a pair of medial setae. In addition, the mucro of X. changlingensis is straight and thin, but lacking teeth. Body length up to 0.81 mm. Body color in alcohol red-brown. Antennal segment I with 7 setae, antennal segment II with 12 setae. Sensory organ of antennal segment III consists of 2 microsensilla, embedded in a tegumentary fold and flanked by 2 longer guard sensillum. Antennae IV with a simple apical bulb and 4 weakly thickened sensillum, of which 3 dorso-external and 1 dorsointernal, and 2 internal sensillum, thinner and longer than the others (Fig. 11). External maxillary lobe with 3 sublobal hairs.
Chaetotaxy, consisting of short setae and longer and fine sensorial setae. Dorsally head without seta c 1 , with both p 1 and p 2, l1 longer than l3 (Fig. 14), thoracic segments II-III with medial setae in 3 rows, seta p2 on tergite of tho-racic segments II-III set in front of p1, on thoracic segments III a2 displaced distally relative to a1 (Fig. 15), on abdominal segments I-III, p5 present, abdominal segments IV without a3, abdominal segments V without a2 (Fig. 16). Ventrally head with seta p1 (Fig. 17), thoracic segments II and III with a pair of medial setae, abdominal segment II without p2 and a5, abdominal segment III with 1 median seta above the retinaculum (Fig. 18), abdominal segment IV without m1 (Fig. 19).

Comment
The new species is distinguished from other species of Xenylla by possessing a mucro without teeth, dorsal side of head with c1 (p1 a/c Babenko et al. 1994) seta absent, seta p2 on tergite of thoracic segments II-III set in front of p1 seta, thoracic segments II and III with a pair of ventral medial setae, abdominal segment II without ventral setae p2 and a5, abdominal segment III with 1 median ventral seta above the retinaculum, abdominal segment IV without ventral seta m1, unguis lacking teeth.

Etymology
Named changchunensis alluding to Changchun, the city where the species was found.