Nemoura sichuanensis, Li & Yang, 2006

Nemoura sichuanensis Li & Yang, 2006:59

Nemoura sichuanensis: Wang, 2007:66

Nemoura sichuanensis: Yang et al., 2015:385

Nemoura hugekootinlokorum: Wang, 2021 in: Wang & Cui, 2021:4. syn. nov.

Materials examined: 2 males, China: Sichuan Province, Roadside 40 km from Yajiang county to Kangding City, 3700m, 1996-VI-15, leg. Yu-Zhou Du ; 10 males, 5 females, Sichuan, Luding County, Yajiageng, 3646m, 2009-VII-4, leg. Yu-Han Qian ; 2 males, Sichuan, Pingwu County, Wanglang National Nature Reserve, Dawodang, 2979m, 33.010833N, 104.156944E, 2016-VII-19, leg. Yu-Zhou Du & Meng-Yuan Zhao ; 1 male, 2 females, Sichuan, Luding County, Yajiageng, 3816m, 29.893192°N, 102.011547°E, 2024-VII-6, leg. Ya-Fei Zhu & Xiao Yang. 1 male, 2 females, Sichuan, Kangding City, Daobangou, 3730m, 30.039931°N, 101.837603°E, 2024-VII-7, leg. Ya-Fei Zhu & Xiao Yang. All specimens are deposited at ICYZU.

Adult habitus: Head dark brown, compound eyes dark, antennae brown; head slightly wider than pronotum (Figs. 1B, 1D, 2B, 2D). Pronotum subquadrate with darker rugosities present (Figs. 1B, 1D, 2B, 2D). Mottled wings, with light spots, veins brown; Legs light brown, with a small yellow band in the middle of the femora (Figs. 1–2).

Male: Body length 4.6–5.2 mm, forewing length 5.8–6.4 mm, hindwing length 4.9–5.4 mm (n=10). Tergum 9 weakly sclerotized, constricted medially, and with several tiny spines and 2–6 long hairs medially (Figs. 3A–C). Sternum 9 with a slender vesicle, length approximately 3X width, slightly constricted basally, mostly membranous; hypoproct broad and semielliptical, tapering posteromedially to a slender tip (Figs. 4A–F). Tergum 10 mostly sclerotized, with a longitudinal median concavity bearing several tiny, black spines located along anterolateral margin (Figs. 3A–C). Cerci sclerotized except at the membraneous apex, slightly curved medially and narrowing toward tip, with a sharp spine and a curved spine at the apex (Fig. 5A); curved spine exhibits variable, ranging from unmodified (Figs. 5A–B), to rough edges with small teeth (Figs. 5E–F), to bifurcating into two spines (Fig. 5C–D). Epiproct elongate (Figs. 6A, 6C, 6E6), with a slender basal cushion, slightly outcurved apical sclerites (Figs. 6A–B) and a small, subapical small ring (Figs. 3A–B, 6A–B); dorsal sclerite weakly sclerotized, with two nearly trapezoidal sclerites along the lateral margin medially (Figs. 6A–B); ventral sclerite prominently sclerotized, with a slender basal plate that bears a tuft of long bristles (Figs. 6C–D). Paraprocts divided into two lobes; inner lobe is a sclerotized strip, tapering apically (Figs. 7A–C); inside portion of inner lobe distinctly sclerotized and attached to apex of hypoproct; basolaterally sclerotized and curved, attached to outer lobe (Fig. 7C); outer lobe mostly sclerotized, mitten-shaped, the inner side is weakly sclerotized and connected to inner lobe, while the outer side sclerotized with pronounced sclerotization near cerci (Fig. 7D).

Female: Body length 4.7–6.1 mm, forewing length 6.9–7.2 mm, hindwing length 5.9–6.3 mm (n=9). Sternum 7 extended medially forming a well-developed pregenital plate with a broad base and a tongue-shaped distal portion, which is strongly sclerotized, overlapping sternum 8 completely and reaching anterior margin of sternum 9 (Figs. 8A–D). Sternum 8 more compact, with a strongly sclerotized subgenital plate located beneath the pregenital plate (Fig. 9A); subgenital plate is roughly triangular in shape, connecting to spines on both sides (which are part of the vaginal cavity and are attached to the vaginal lobes rather than firmly connected to the subgenital plate); vaginal lobes on sternum 8 not obvious, but can be recognized as paired strips (Fig. 9B); Sternum 9 extended anteromedially, trapezoidal (Fig. 8).

Distribution: China (Sichuan Province).

Remarks. There is a significant degree of intraspecific morphological variation exhibited by this species, namely the epiproct ventral sclerite, overall epiproct shape, paraproct inner lobe, and cerci. For example, the ventral sclerite has a tuft of long bristles of varying number (Figs. 6C–D). These bristles will become lighter and even partially shed when they are soaked in NaOH. The epiproct also exhibits differences in shape, with one form being broader apically and narrow basally (Fig. 3C), while another is more uniform (Figs. 3A–B), as described by Li & Yang (2006), throughout its length. Inner lobe tightly connected to the tip of hypoproct (Figs. 4B–F); In some individuals, their color is similar, which is easy to be mistaken for a whole (Fig. 4B, 4C); in others it is completely the opposite (Fig. 4D, 4E, 4F). Inner lobe and the tip of hypoproct are sometimes not clearly separated (Fig. 4A) and can be obscured by the base of hypoproct, and they will be completely separated after prolonged immersion in NaOH (Figs. 7B–C). The curved spine of the cerci also exhibits considerable variation, as unmodified in some specimens (Figs. 5A–B), while others have rough edges with teeth (Figs. 5C–D), or bifurcating into two spines (Figs. 5E–F) as described by Li & Yang (2006).

The original description by Li & Yang (2006) did not mention the ventral sclerite bearing a tuft of long bristles nor inner paraproct lobe as a narrow, sclerotized strip. Due to this, we think that this may be due to a structural absence one the holotype itself damage caused by anatomical manipulation, or simply an omission during observation. Overall, because the description of N. sichuanensis was based on only the holotype male, subtle differences between individuals or populations of this species could not be identified. Additionally, sequencing the mitochondrial cooxidase 1 subunit gene (i.e., mtCOI or barcoding) is not suitable for specimens that have been soaked and preserved for nearly 20 years. Therefore, we believe the best approach is to return to the type locality and conduct resampling to obtain a sufficient amount of reliable material for a more thorough revision. This approach has been successfully applied in other families of Chinese stoneflies (Huo et al. 2021, Huo et al. 2023, Zeng et al. 2024).

Comparative morphological studies have shown that the specimens collected from various areas of Sichuan have the same characteristics fit the diagnosis of N. sichuanensis and are also consistent with the description of N. hugekootinlokorum . Therefore, we consider that N. hugekootinlokorum is a synonym of N. sichuanensis .

In addition, the so-called " N. hugekootinlokorum " were collected in mid-March, while the specimens of N. sichuanensis we examined were collected in June to July, This suggests that the emergence time of this species is longer. There are still several adults active in the area until June to July, suggesting that the emergence periods lasts for at least three months.