Nemoura lixiana sp. nov.

urn:lsid:zoobank.org:act: 1532 AE67- 2249 -4AFA-B935-03AF014801EE

Figs 1–5, 7

Diagnosis

Nemoura lixiana sp. nov. exhibits the typical body color and genitalic characters of genus Nemoura (Figs 2–5). The new species is most similar to Nemoura geei Wu, 1929 by sharing similar characteristics of male epiproct and female pregenital plate (Shimizu 1997; Teslenko & Zhiltzova 2009; Yang et al. 2015). However, males of the new species can be distinguished from N. geei by the presence of extra stout spines on inner membrane of cerci (Figs 2C, 3A, 4E), which are absent in N. geei (Fig. 6 A–C); the median lobe of paraprocts is projected inwards and covers half of inner lobe in N. lixiana sp. nov. (Fig. 4E), but hardly reaches the inner lobe in N. geei (Fig. 6 A–C); in the epiproct of N. lixiana sp. nov., the dorsal sclerite has two apparently angled lateral sclerites which are thick, with transverse anterior margins and very stout posterior humps (Fig. 4B), while in N. geei, the lateral sclerites are thinner and not angled, with oblique anterior margins and low posterior humps (Fig. 6 D–F). The females of N. lixiana sp. nov. have two oval lateral sclerites on sternum 8 but without small lateral pits on sterna 7–8 (Fig. 5 B–C), whereas in N. geei, sternum 8 has two long transverse sclerites and sterna 7–8 have paired lateral pits (Fig. 6 G–H). In addition, type locality of N. lixiana sp. nov. is in southwestern China (Fig. 1), which is apparently isolated from the known ‘northeastern Asian’ distribution of N. geei in Beijing, Henan, Shandong, Inner Mongolia, Korea, Japan and the Russian Far East (Yang et al. 2015; DeWalt et al. 2020).

Etymology

The new species is named after the type locality, Lixian County.

Material examined

Holotype

CHINA • ♂; Sichuan Province, Lixian County, side of Xuemeng Road, a small unnamed stream (Fig. 7); 31°33′56′′ N, 103°17′32′′ E; 1634 m a.s.l; 5 Oct. 2019; Zhi-Teng Chen leg.; ICJUST.

Paratypes

CHINA • 8 ♂♂, 4 ♀♀; same collection data as for holotype; ICJUST.

Description

Male

MEASUREMENTS. Holotype: BL = 3.5 mm; FL = 6.3 mm; HL = 4.5 mm. Other specimens: BL = 3.5‒4.5 mm; FL = 6.0‒7.0 mm; HL = 4.5‒6.0 mm.

HEAD (Fig. 2 A‒B). Head dark brown; two ocelli pale; compound eyes dark and protruded; antennae slender and dark brown, much longer than body length; mouthparts brown.

THORAX (Fig. 2 A‒B). Brown. Pronotum brown, with dark rugosities, corners angulate; anterior margin arcuate, posterior margin concave. Legs pale brown, joints of each segment darker.

WINGS (Fig. 2 A‒B). Macropterous, wing membrane subhyaline, veins brown; margins of wings fringed with short bristles.

ABDOMEN (Figs 2‒4). Abdominal segments generally pale brown; abdominal terga with an obscure longitudinal stripe. Posterior margin of tergum 9 with a row of long bristles. Tergum 10 with a membranous median area anterior of median area, with two small lateral patches of sensilla basiconica; posterior margin of tergum 10 with two sclerotized coniform lobes. Cerci prolonged and upcurved, covered by dense long hairs; inner part membranous, subapically with a stout inner spine; outer surface of cerci sclerotized, outer sclerite kidney-shaped, subapically with a small back-curved spine.

GENITALIA (Figs 2 C‒E, 3‒4). Dorsal sclerite of epiproct with two elbow-shaped, dark lateral sclerites; inner apex of each lateral sclerite forked; apex of epiproct with a prolonged median sclerite covered by membrane; ventral sclerite with a C-shaped base and two sinuous lateral sclerites, which project forwards and form two apically dentate arms, the arms each with three or four apical teeth. Vesicle of sternum 9 mostly membranous, claviform and slightly constricted basally; hypoproct broad and elliptical, apex extended backwards, with a long triangular sclerite. Paraprocts bilobed; inner lobe weakly sclerotized, finger-shaped with a blunt tip, near half as long as outer lobe; outer lobe strongly sclerotized, broad basally, posteromedial margin forming a long triangular sclerite, inner margin with a projected basal hump covering half of inner lobe. The accidently extruded aedeagus in a paratype cylindrical, mostly membranous, apex with one or two obscure small lobes.

Female

Similar to males in body coloration (Fig. 5A).

MEASUREMENTS. BL = 4.5‒5.2 mm; FL = 7.0‒ 8.5 mm; HL = 6.0‒ 7.5 mm.

GENITALIA (Fig. 5 B–C). Pregenital plate of sternum 7 rounded and sclerotized, reaching half-length of sternum 8. Sternum 8 with two oval-shaped, dark brown lateral spots. Paraprocts near trapezoidal and fused basally.

Distribution

China: western Sichuan Province (Fig. 1).

Remarks

This species was collected in the afternoon of 5 Oct. 2019, when the adults were emerging massively. The habitat, a very small unnamed stream flows down from a dried mountain (Fig. 7), geographically isolated from other known water systems. An undescribed new genus of Elmidae (Coleoptera) was simultaneously collected in this unique stream, but no mayflies or caddisflies or other aquatic insects were found at that time.