Epeorus (Iron) aesculus Imanishi, 1934 (Figs 23–27)

[Japansese name "Kiiro-hirata-kagerou"]

Epeorus aesculus Imanishi, 1934: p. 382, fig. 1, pl. 18, fig. 1 (male imago, female imago, nymph) [JAPAN: Toyama (type locality), Kyoto, Shiga]; Imanishi 1940: p. 250, fig. 34 (nymph) [KOREA]; Uéno 1950: p. 123, fig. 308 (male imago, female imago) [JAPAN]; Tshernova 1952: p. 251 (nymph) [RUSSIA: Sakhalin]; Uéno 1959: p. 53 (nymph) [JAPAN]; Gose 1962: p. 20, fig. 1-11-3 (nymph) [JAPAN]; Gose 1979: p. 44, figs 11, 19 (male imago, nymph) [JAPAN]; Gose 1985: p. 16, fig. 36 (nymph) [JAPAN]; Ishiwata 2002: p. 21, figs 165, 166 (nymph, male imago) [JAPAN: Kanagawa]; Ishiwata & Takemon 2005b: p. 105, figs 45-2, 47-2 (male imago, nymph) [JAPAN]; Maruyama 2016: p. 171, figs 1-171a, 1-172, 1-253, 1-254, 1-255, 1-256 (male imago, female imago, male subimago, female subimago) [JAPAN: Hyogo]; Ishiwata et al. 2018: p. 126, figs 45-2, 47-2 (male imago, nymph) [JAPAN]; Ishiwata & Fujitani 2018: p. 32, pl. 21, figs 1, 2 (egg) [JAPAN].

Epeorus (Epeorus) aesculus: Koss & Edmunds 1974: p. 314, pl. 8, fig. 92 (egg).

Iron aesculus: Sinitshenkova 1978: p. 50 (male imago, nymph) [Far East RUSSIA]; Tshernova et al. 1986: p. 120, fig. 53-1 (male imago) [Far East RUSSIA]; Quan et al. 2002: p. 254, figs 37, 49, 78, 93 (nymph) [Northeast CHINA].

Epeorus (Iron) aesculus: Byong & Bae 1984: p. 7, pl. 4, figs a–g (male imago, nymph) [KOREA]; Bae et al. 1998: p. 91 (imagines, nymph) [KOREA, Far East RUSSIA].

Iron grunini Sinitshenkova, 1982: p. 59, fig. 3 (male imago, female imago, female subimago) [Far East RUSSIA], synonymized by Kluge & Tiunova 1989: p. 8.

Iron levanidovae Sinitshenkova, 1982: p. 60, fig. 4 (male imago, female imago, female subimago, nymph) [Far East RUSSIA], synonymized by Kluge & Tiunova 1989: p.8.

Iron koreanicus Braasch & Soldán, 1988: p. 25, figs 1-1–1-8 (nymph) [KOREA], synonymized by Bae et al. 1998: p. 91.

Materials examined. Type specimens: We could not find the holotype at The Kyoto University Museum in 2019. Probably lost. Other specimens: JAPAN, HOKKAIDO, ISHIKARI: [1.] Sapporo-shi, Minami-ku, Jozankei, Toyohira-gawa Riv., mainstream, 678 m a.s.l. (42°47'57.0"N, 141°10'14.3"E), 3 mature male nymphs and 2 mature female nymphs, 11.VI.2003, K. Saito; [2.] Sapporo-shi, Minami-ku, Jozankei, Izarisawa-gawa Stream (a tributary of Toyohira-gawa Riv.), 568 m a.s.l. (42°51'18.4"N, 141°10'34.0"E), 53 mature male nymphs and 44 mature female nymphs, 14.VI.2007, K. Saito; [4.] Sapporo-shi, Minami-ku, Jozankei, Usubetsu-gawa Stream (a tributary of Toyohira-gawa Riv.), 472 m a.s.l. (42°54'33.5"N, 141°07'28.9"E), 5 mature male nymphs, 06.VII.2002, K. Saito; [5.] Sapporo-shi, Minami-ku, Jozankei, Shirai-gawa Stream (a tributary of Toyohira-gawa Riv.), the confluence of Shirai-gawa Stream and Migimata-gawa Stream, 450 m a.s.l. (42°59'39.6"N, 141°04'42.9"E), 5 mature male nymphs and 4 mature female nymphs, 06.VI.2004, K. Saito; ditto, 1 immature nymph, 07.IV.2019, T. Takayanagi; [6.] Sapporo-shi, Minami-ku, Jozankei, Otarunai-gawa Stream (a tributary of Toyohira-gawa Riv.), 502 m a.s.l. (43°04'22.4"N, 141°06'34.8"E), 8 mature male nymphs and 15 mature female nymphs, 11.V.2002, K. Saito; [8.] Sapporo-shi, Minami-ku, Jozankei, Shirai-gawa Stream (a tributary of Toyohira-gawa Riv.), 300 m a.s.l. (42°58'37.7"N, 141°08'16.4"E), 6 mature male nymphs and 8 mature female nymphs, 14.VI.2005, K. Saito; [10.] Sapporo-shi, Minami-ku, Toyama, Kannonzawa-gawa Stream (a tributary of Toyohira-gawa Riv.), 267 m a.s.l. (42°58'31.0"N, 141°15'30.0"E), 9 male imagines and 2 female imagines, 23.V.2019, T. Takayanagi; ditto, 5 mature male nymphs and 1 mature female nymph, 10.V.2020, T. Takayanagi; ditto, 1 female imago, 29.V.2020, T. Takayanagi; [11.] Sapporo-shi, Minami-ku, Toyotaki, Toyohira-gawa Riv., mainstream, 188 m a.s.l. (42°57'38.4"N, 141°13'50.9"E), 1 mature male nymph, 14.VI.2005, K. Saito; [13.] Sapporo-shi, Minami-ku, Makomanai, Toyohira-gawa Riv., mainstream, 68 m a.s.l. (42°59'58.5"N, 141°20'26.0"E), 1 mature male nymph, 26.VI.2006, K. Saito; [15.] Sapporo-shi, Chuo-ku, Minami 13-jo, Nishi 1-chome, Toyohira-gawa Riv., mainstream, 28 m a.s.l. (43°02'35.3"N, 141°21'31.7"E), 1 mature male nymph, 16.V.2020, T. Takayanagi; [18.] Sapporo-shi, Nishi-ku, Heiwa, Kotonihassamu-gawa Stream (a tributary of Shin-kawa Riv.), 312 m a.s.l. (43°03'25.3"N, 141°12'40.6"E), 4 mature male nymphs and 4 mature female nymphs, 03.V.2020, T. Takayanagi; [19.] Chitose-shi, Shikotsuko-onsen, Shirisetsunai-gawa Stream (an inlet stream of Lake Shikotsu-ko), 289 m a.s.l. (42°46'39.0"N, 141°24'05.8"E), 1 mature male nymph, 23.V.2019, T. Takayanagi; ditto, 6 female imagines and 1 mature male nymph, 01.VI.2021, T. Takayanagi; [20.] Chitose-shi, Bifue, Bifue-gawa Stream (an inlet stream of Lake Shikotsu-ko), 257 m a.s.l. (42°43'47.9"N, 141°15'18.2"E), 1 mature female nymph, 07.IV.2019, T. Takayanagi; OKHOTSK (outside of the study area): Engaru-cho, Mt. Hirayama, small stream flowing into Shiyuubetsu-gawa Riv., 1164 m a.s.l. (43°46'15.6"N, 143°01'43.5"E), 5 male imagines, 12.VII.2018, T. Takayanagi .

Nymph (mature, in ethanol), redescription (Figs 23–25).

Body length 8.1–9.0 mm (male), 8.3 mm (female). Cercus length ca. body length x 1.1.

Head. Shape trapezoidal. Color pale-brown to dark-brown, with white markings. Compound eyes dark gray. Ocelli dark gray. Antennae brown. Anterior margin densely covered with fine hair-like setae extending to lateral margins. Dorsal surface of head covered with fine hair-like setae (Figs 24a, b). Labrum: anterior and lateral margins evenly convex, anterior margin gently concave. Ventral surface with a row of bristles along lateral margins extending to anterior margins, with a row of short setae and brush of median fine hair-like setae on each side. Dorsal surface with six widely spaced long bristles medially, two long bristles near side of each antero-lateral margin, and scattered setae of variable lengths (Fig. 25a). Mandibles: each outer incisor with two apical teeth and serrated margins, inner incisor both straight with two apical teeth (right mandible) or three apical teeth (left mandible) and sharply serrated on outer margin of both incisors. Tuft of long setae on the base of both incisors and one brachy-pulmose seta on the base of left incisor (Figs 25b, c). Maxillae: One penicillate seta and one or two long, thick setae at base of apical tooth complex (Fig. 28e). Hypopharynx: Superlinguae distally widened. Lingua subquadrate. Labium: labial palps two segmented, outer margin of proximal one with sparse-thick setae. Distal segment with sparse, hair-like setae on outer surface and dense, brush-like setae on distal 1/3 area.

Thorax. Dorsally pale-brown to dark-brown, ventrally white (Fig. 23). Pronotum slightly expanded laterally (Fig. 29d). Blackish spot on propleuron, just posterior to fore coxa (Figs 23c, f). Legs. Each femur with dark brown markings and a hypodermal black spot on middle part of anterior face (Fig. 24c), blade-like long setae on dorsal edge, short bluntly pointed spines on ventral edge. Femoral setae dense and diversely shaped: semi-oblong, oval, semi-circular or spatulate (Fig. 25d). Tibia with two dark-brown markings, long hair-like setae on its dorsal edge (Fig. 24c). Tarsus darker in proximal area, with long hair-like setae on its dorsal edge (Fig. 24c). Tarsal claw with 3–4 small denticles.

Abdomen. Terga pale-brown to dark-brown, each tergum with a pair of dark obscure spots. Terga I–VII have a black streak on both latero-posterior edges (Figs 23a, d). Sterna yellowish-brown (Figs 23b, e). Each tergum with dense, long hair-like setae on the surface of midline. Posterior margin of each tergum without long setae, with short, blunt spines which overlap in 3–4 levels (Figs 25j, 31e). Each tergum I–VII with three postero-lateral projections, ventral and dorsal ones blunt and lateral one short-tipped (Fig. 30e). Posterior margins of sternum IX rounded with deep and wide medial emargination, covered with long hair-like setae (Figs 25h, i). Dorsal surface of cercus with a row of fine setae. Gills. Color whitish or pale brownish, costally brown (Fig. 24d). Gill I slightly expanded anteriorly (Figs 24d, 25e). Gills II–VII oval (Figs 24d, 25f, g). Costal margin of gill I with fine setae. Costal margin of gills II–VII with small spines and fine setae forming a rough surface. Each gill plate with filaments forming a fan-shape together. Gill VII with longitudinal fold (Fig. 25g).

Male imago (in ethanol), redescription (Fig. 26).

Body length 9.1–10.9 mm. Cercus length ca. body length x 3.2. Forewing length 10.0– 12.3 mm.

Head. Yellowish-brown. Frons shape triangular. Compound eyes dark-gray, light-blueish-gray when alive. Ocelli grayish-white with dark-gray border.

Thorax. Ground color yellowish-brown, internal tissues visible. Pronotum, mesonotum and metanotum without markings. Distinct blackish spot on posterior part of propleuron. Meso- and meta-pleura without markings (Fig. 26a). Wings. Hyaline. Forewing veins white, subcosta to radius slightly dark colored, pterostigmatic area cloudy. No markings on both fore and hindwing (Fig. 26e). Legs. Anterior face of each femur with black spot on middle part and blurred black line on proximal half. Joints of fore tibiae and tarsi dark. Fore tarsal segments becoming shorter distally, each joint dark. Tarsal claws dissimilar, one hooked-shape and the other oblong (Figs 26b–d).

Abdomen. Yellowish brown, transparent. Posterior margin of terga I–IX edged with black streaks which are darker laterally (Fig. 26a). Posterior margin of styliger plate rounded, without projection on forceps base. Penis lobes with proximally oriented spines and complex projections, titillators developed, curved outward (Fig. 26f). Cercus brown.

Female imago (in ethanol), redescription (Fig. 27).

Body length 8.3–8.4 mm. Cercus length ca. body length x 2.3. Forewing length 10.0– 11.6 mm.

Head. Yellowish-white. Compound eyes gray to dark-gray. Ocelli as in male imago.

Thorax. Coloration as in male imago (Fig. 27a). Wings. Veins darker than males (Fig. 27a). Legs. Coloration and markings as in male imago. Fore tarsus not elongated. Fourth segment of each tarsus shortest, other segments almost equal lengths. Tarsal claws dissimilar as in male imago (Figs 27b–d).

Abdomen. Coloration and markings as in male imago. Eggs yellowish and visible when living. Posterior margin of subgenital plate rounded. Posterior margin of sternum IX with deep and wide emargination (Fig. 27e).

Diagnosis and comparison. Nymph. This species and E. curvatulus both have anteriorly extended gill I; however, in this species, the gills do not meet beneath the mesothorax. Male Imago. Wings without black markings. Penis has titillators and well-developed latero-dorsal spines. There are no similar species in the study area.

Remarks. Nymph. The specimens identified here as E. aesculus match the original description by Imanishi (1934). Imanishi described two forms of this species based on the shape of gill I: a "small gill type " and a "large gill type." The specimens examined in this study correspond to the former. No similar species are found in the study area. Imagines. The specimens identified here as E. aesculus agree with the original description (Imanishi 1934). Subgenus attribution. This species should be classified under the subgenus Iron based on the following features: 1) gill I is expanded anteriorly in the nymphal stage (Figs 24d, 25e); 2) hairs on the anterior margin of the head are directed forward in the nymphal stage (Figs 24a, b); and 3) the male imago has a penis with titillators and well-developed latero-dorsal spines (Fig. 26f) (Kluge 2004).

This species was originally described based on male imaginal, female imaginal, subimaginal, and nymphal specimens collected in the Goro-sawa Valley, Toyama, central Honshu (Imanishi 1934).Although the type specimens were lost, specimens likely identified by Imanishi himself are available in the collection of The Kyoto University Museum (Author's investigation 2019). Imanishi (1934) described two types of nymphal gill I shapes, a "small-sized" type and a "large-sized" type, and the specimens observed in this study corresponding to the former. This variation may represent two different species, with the "small-sized" type corresponding to E. (Iron) aesculus and the "large-sized" type to E. (I.) maculatus Tshernova, 1949 (Sinitshenkova 1978). Kluge & Tiunova (1989) reviewed Asian species and recognized three distinct species: E. (I.) aesculus, E. (I.) maculatus, and E. (I.) alexandri Kluge & Tiunova, 1989 . The morphological descriptions of E. (I.) aesculus by Sinitshenkova (1978) and Kluge & Tiunova (1989) align with E. (I.) aesculus as described here, with only a slight difference in coloration.

Emergence periods and habitat. Imagines emerge from May to June in the study areas. This species is mostly caught in mountain streams (localities [1.], [2.], [4.]–[6.], [8.], [10.], [18.]–[20.]).

Distribution. Japan (Hokkaido, Honshu, Shikoku, and Kyushu), Korea, China (Northeast), and Russia (Far East).