Holotype. 1 male, China: Qinghai province, Huangzhong county, Shuixia, 101°41.25'E, 36°82.46'N, 2590 m, 8 August, 2015, leg. Yu-Zhou Du. Paratype: 1 male and 7 females, the same locality and data as holotype, leg. Yu-Zhou Du, Zhi-Hou Li, Qiu-Yu Fan.

This species is characterized by a pale head, a pale pronotum disc with median stripe and brown margins, and the abdominal terga 1–8 with a longitudinal stripe. Epiproct mostly sclerotized and hairless, sub-triangular in dorsal view with a blunt tip. Aedeagus ventrally with two median situated elliptical lobes.

This new species is most similar to H. valentinae Stark & Sivec, 2009, known from Sichuan Province, China, but differs in the formation of the epiproct, which is mostly sclerotized and hairless in H. triangulata sp. n., whereas it is with sclerotized margins, membranous posterodorsal area and sparse patch of setae in H. valentinae (see Figs 13 and 17 in Stark and Sivec 2009). Besides, the subgenital plate of female is originating from tergum 8 to the posterior margin of tergum 9 in H. triangulata, while it’s slightly produced as a small rounded lobe with long setae in H. valentinae (see fig. 15 in Stark and Sivec 2009). The details of the wing venation and aedeagus are not described for H. valentinae.

Triocellate. General color light yellow patterned with dark brown. Head mostly pale yellow without any markings; compound eyes and ocelli black (Fig. 1). Pronotum hyaline, with median stripe and brown margins; meso- and metanota with dark brown W-shaped markings. Wings hyaline; Rs of both wings branched; A₃ of forewing fused with A₂ near base; anal field of hindwing small and folded with three veins (Fig. 8). Coxae, tibiae and femura pale, tarsi brown. Abdominal terga 1–8 with a medial wide stripe. Cerci yellowish-brown with long brown setae (Figs 9, 10).

Figures 1–4. 

Haploperla triangulata sp. n. 1 Head and pronotum, dorsal view 2 Male terminalia, dorsal view 3 Male terminalia, ventral view 4 Male terminalia, lateral view.

Figures 5–8. 

Haploperla triangulata sp. n. 5 Aedeagus, lateral view 6 Aedeagus, ventroapical view 7 Female subgenital plate, ventral view 8 Wings.

Figures 9–10. 

Haploperla triangulata, sp. n. 9 Male habitus, dorsal view 10 Female habitus, dorsal view.

Forewing length 6.5–7.0 mm, hindwing length 5.5–6.0 mm. Posterior margin of tergum 9 dark and slightly concave, covered with fine hairs. Tergum 10 divided (Fig. 2). Subgenital plate arising from tergum 9 to tip of the abdomen, slightly tapering at tip (Fig. 3). Subanal process simple, pale and subtriangular in shape. Epiproct mostly sclerotized and hairless, sub-triangular in dorsal view with a blunt tip (Figs 2, 4). Aedeagus membranous and curved ventrally, ventrally with two median situated elliptical lobes, subapically with a plump lobe (Figs 5, 6).

Forewing length 7.0–7.5 mm, hindwing length 6.0–6.5 mm. General pattern similar to males. Abdominal segments 1–8 with median brown strip (Fig. 10). Ventral surface and terminalia without markings. Subgenital plate distinct, originating from tergum 8 to the posterior margin of tergum 9; posterior margin slightly protruding, forming a blunt lobe (Fig. 7).

The species epithet refers to the sub-triangular shape of the epiproct.

China (Qinghai province).

We describe a new species of the genus Haploperla, thereby increasing the total number of Haploperla species recorded in China to five. More Haploperla species are expected to be found in China in the future because the geographical conditions ensure suitable resources for stoneflies. More studies are needed to enrich our understanding of Haploperla.