Siphlonurus davidi (Navás, 1932) Figures 3–4 Siphluriscus? davidi Navás, 1932: 929 (male subimago, from Sichuan Province, China). Siphluriscus davidi: Wu 1935: 251; Gui 1985: 80. Siphlonurus davidi: Zhou & Peters 2003: 346; Sartori & Peters 2004: 2 (type re-description); Han et al. 2016: 38 (adult and nymph, re-description); Zhou 2013: 204 (list); Zhou et al. 2015: 254 (list); Yang et al. 2023: 121 (comparison). Material examined: 65 nymphs, 3♀ imagos, 1♂ imago, Jiuzhaigou Valley Scenic and Historic Interest Area, Aba Tibetan and Qiang Autonomous Prefecture, Sichuan Province, 33.159°N, 103.901°E, ca. 2400 m, 6–7.VII.2013, Beixing Wang, Yun He, and Guangba Li; 130 nymphs, Jiuzhaigou Valley Scenic and Historic Interest Area, Aba Tibetan and Qiang Autonomous Prefecture, Sichuan Province, 33.159°N, 103.901°E, ca. 2400 m, 9–12.VII.2019, Beixing Wang, Xinyu Ge, and Yu Wang; 1♀ imago, 1♂ imago, Jiuzhaigou Valley Scenic and Historic Interest Area, Aba Tibetan and Qiang Autonomous Prefecture, Sichuan Province, 33.1715°N, 103.52108°E, ca. 2400 m, 6.VII.2023, Mengyao Li. Description: see Han et al. (2016). Distribution: China (Sichuan). Diagnosis Mature nymph: Body length 13.0–17.0 mm, wingpads with spots (Figs 3A, B). Length ratio of first segment of maxillary palp to galea-lacinia about 1.0: 1.0, inner margin of maxillary palp segment II straight (Fig. 3C). Posterolateral spines on terga I–IX gradually larger from anterior to posterior, length ratio of posterolateral spine on tergum IX to its tergum = 1.0: 2.0 (Figs 3D–F). Each abdominal sternum with pair of fused reddish-brown oblique stripes (Fig. 3B). Posterior margin of abdominal sternum IX distinctly convex (Figs 3E, F). Both dorsal surface and margins of tergum X with stout and pointed spine-like setae (Fig. 3G). Outer margins of dorsal lamellae of both gills I and II straight while those of ventral lamellae concave, costal rib of dorsal lamella in gill II longer than half of anterior margin (Figs 3H, I). Outer and posterior margins of gill III straight, proximal plate of gill VII well developed (Figs 3J, K). Male imago: Body length 13.0–16.0 mm, forewing with dark brown crossveins and large dark brown spots between C and Rs 1, distal half of hindwing light brown with a spot near middle of R 1 and a brown stripe near forking point of MA. Forelegs entirely brown, midlegs and hindlegs entirely light brown (Figs 4A–C). Anterior and lateral margins of each abdominal sternum darker (Fig. 4D). Posterolateral spines of abdominal segments VIII and IX relatively small (Figs 4D–G). Inner margin of basal segment of forceps without projection, length of penis subequal to styliger (Figs 4F, G). Dorsal elongation of penis straight and spineless with sclerotized outer margin, dorsal sclerotized transverse band of penis without expansion, each penis lobe tip with brown sclerotized plates, length of two penis lobes ca. 1.1x width (Figs 4H, I). Female imago: Body length 15.0–16.0 mm, wings with brown stripe and dots. Color pattern similar to male. Sternum VII extended posteriorly into a rectangular lobe, sternum VIII with a pair of reddish-brown stripe (Fig. 4J). Remarks For morphological comparison of three closely related species (S. davidi, S. dongxi, and S. orientalis sp. nov.) see remarks of S. orientalis sp. nov. Three diagnostic characteristics proposed by Yang et al. (2023) for distinguishing between S. dongxi and S. davidi appear to be problematic: (1) Sclerotization of penis lobe: Yang et al. (2023) proposed that two elongations on transverse sclerite of penis lobes could serve as a diagnostic feature for male S. dongxi. However, further observations reveal that dorsal sclerotization pattern of penis lobes is similar across all three species (S. davidi, S. dongxi, and S. orientalis sp. nov.). This pattern includes a pair of rounded sclerotized plates and a medially convex transverse sclerotized band, and each rounded plate with a small apical elongation (Fig. 4H); (2) Posterolateral spines on tergum IX in male adults: While Yang et al. (2023) proposed that male imagos of S. dongxi can be distinguished from S. davidi by well-developed posterolateral spines on tergum IX, our observations indicate that all three species (S. dongxi, S. davidi, and S. orientalis sp. nov.) exhibit relatively small spines compared to S. immanis. (3) Posterolateral spines on terga in nymph: Yang et al. (2023) stated that posterolateral spines on the terga of S. dongxi nymph are restricted to segments II–IX, but this may require reconsideration. All reported Siphlonurus nymph in China possess posterolateral spines on abdominal terga I–IX. Additionally, posterolateral spines of these three species (S. davidi, S. dongxi, and S. orientalis sp. nov.) are relatively large, with a spine-to-tergum IX length ratio of approximately 1.0: 2.0.

Published as part of Qiang, Xin-He & Zhou, Chang-Fa, 2025, The species diversity and phylogeny of the genus Siphlonurus Eaton, 1868 from China (Ephemeroptera: Siphlonuridae), pp. 1-56 in Zootaxa 5711 (1) on pages 8-11, DOI: 10.11646/zootaxa.5711.1.1, http://zenodo.org/record/17882788