Siphlonurus immanis Kluge, 1985 Figures 7–8 Siphlonurus chankae: Bajkova, 1979: 53 (nec Siphlonurus chankae Tshernova, 1952) (nymph from Russia). Siphlonurus immanis Kluge 1985: 18 (imagos and nymph from Russia); Hwang & Bae 2001: 47 (nymph); Quan et al. 2002: 258 (first record from China); Tiunov & Tiunova 2007: 23; Zhou 2013: 204 (list); Zhou et al. 2015: 254 (list). Material examined: 15 nymphs, Sanbao Village, Songfengshan Town, Acheng District, Harbin City, Heilongjiang Province, 1.IV.2023, Qiang Dong; 200 nymphs, 20 nymph exuviae, Erdaohzi, Sanbao Village, Songfeng Mountain Town, Acheng District, Harbin City, Heilongjiang Province, 45.245339°N, 127.263786°E, ca. 260 m, 27–28.IV.2024, Xinhe Qiang, Muhe Deng, and Mengyao Li; 5 nymphs, Dashihe, Xinxing Village, Acheng District, Harbin City, Heilongjiang Province, 45.233113°N, 127.154525°E, ca. 370 m, 29.IV.2024, Xinhe Qiang, Muhe Deng, and Mengyao Li; 3 nymphs, Tangwanghe, Haolianghe Town, Nancha District, Yichun City, Heilongjiang Province, 46.431801°N, 129.374393°E, ca. 110 m, 4.V.2024, Xinhe Qiang, Muhe Deng, and Mengyao Li; 100 nymphs, 50 nymph exuviae, 60 ♀ imagos, 28 ♂ imagos, Erdaohzi, Sanbao Village, Songfeng Mountain Town, Acheng District, Harbin City, Heilongjiang Province, 45.245339°N, 127.263786°E, ca. 260 m, 23–29.V.2024, Xinhe Qiang and Xiaofang Chen. Description: see Kluge (1985, adult and nymph) and Hwang & Bae (2001, nymph). Distribution: China (Heilongjiang Province); Korea; Russia; Mongolia. Diagnosis Mature nymph: Body length 18.0–25.0 mm, wingpads without spots (Figs 7A, 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. 7C). 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 7D–F). Each abdominal sternum with inverted U-shaped marking (Fig. 7B). Posterior margin of abdominal sternum IX nearly straight (Figs 7E, F). Dorsal surface and posterior margin of tergum X with stout and pointed spine-like setae, lateral margins lack (Fig. 7G). Outer margins of dorsal and ventral lamellae of both gills I and II concave, costal rib of dorsal lamella in gill II shorter than half of anterior margin (Figs 7H, I). Outer and posterior margins of gill III concave, proximal plate of gill VII well developed (Figs 7J, K). Male imago: Body length 20.5–22.0 mm, all legs brown (Fig. 8A), wings transparent (Figs 8C, D). Posterolateral spines of abdominal segments VIII and IX relatively large (Fig. 8E, F). Each abdominal sternum with inverted Ushaped marking (Fig. 8F). Inner margin of basal segment of forceps with projection, length of penis subequal to styliger (Figs 8G, H). Dorsal elongation of penis slender and spineless, dorsal sclerotized transverse band of penis without expansion, two penis lobes separated, each tip bifurcated, outer bifurcation distinctly sclerotized, ventral side with a translucent membranous structure, inner margin of each penis lobe with 4–6 small spines basally, outer margin concave near the middle (Figs 8I, J). Female imago: Body length 27.0–29.0 mm, wings transparent (Fig. 8B). Color pattern similar to male (Fig. 8K). Sternum VII extended posteriorly into a triangular lobe, sternum VIII with W-shaped dark brown sclerotized line (Fig. 8L). Remarks: This species is close to S. chankae. The detailed comparison is presented in the remarks of S. chankae.

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 page 14, DOI: 10.11646/zootaxa.5711.1.1, http://zenodo.org/record/17882788