Epeorus (Caucasiron) curvatulus Matsumura 1931
Creators: name: Takayanagi, Tatsushi
name: Yoshizawa, Kazunori
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Ephemeroptera
Heptageniidae
Epeorus
Epeorus curvatulus

description: Epeorus (Caucasiron) curvatulus Matsumura, 1931 (Figs 15–19)
[Japanse name "Uéno-hirata-kagerou"]
Epeorus curvatulus: Matsumura 1931: p. 1477 (male imago) [JAPAN: Tokyo]; Matsumura 1933: p. 97, pl. 21, fig. 13 (male imago) [JAPAN: Honshu]; Ishiwata 2002: p. 21, figs 167–170 (nymph, male imago) [JAPAN: Kanagawa]; Ishiwata & Takemon 2005b: p. 105, figs 45-3, 47-4, 47-5 (male imago, nymph) [JAPAN]; Maruyama 2016: p. 171, figs 1-171c, 1-174, 1-261, 1-262, 1-263, 1-264 (male imago, female imago, male subimago, female subimago) [JAPAN: Hyogo]; Ishiwata et al. 2018: p. 126, figs 45-3, 47-4, 47-5 (male imago, nymph) [JAPAN]; Ishiwata & Fujitani 2018: p. 32, pl.21, fig. 4 (egg) [JAPAN].
Epeorus uenoi auct., non Matsumura, 1933: Imanishi 1934: p. 383 pl. 18, fig. 2 (nymph, male imago, female imago) [JAPAN: Kyoto]; Imanishi 1940: p. 252, fig. 33 (nymph) [JAPAN: Kyoto]; Gose 1962: p. 20, figs 1-11-1a, 1b (nymph) [JAPAN]; Gose 1979, p. 44, figs 8, 10, 22 (male imago, nymph) [JAPAN]; Okazaki 1984: p. 22, fig. 46 (egg) [JAPAN]; Gose 1985: p. 16, figs 34, 35 (nymph) [JAPAN].
Epeorus (Belovius) uenoi: Tshernova 1981: p. 334, fig. 11 (male imago) [JAPAN].
Iron sp.?: Uéno 1928: p. 28, pl. 5, figs 4, 4a–4i, pl. 6, figs 4j–4n (nymph) [JAPAN: Kyoto, Nagano, Toyama].
Materials examined. Type specimen (Holotype): (identification label by Imanishi, 1933 " Epeorus curvatulus Matsumura, K. Imanishi, 1933 "). 1 male imago, "Tamagawa [タマガハ] 7/25 (year not listed)", " Epeorus curvatulus det. Matsumura ", "Two tails color white [二*の¹は̊e]", "Type Matsumura" (red label), " Epeorus curvatulus Matsu. " (probably attached recently) (Fig. 34).
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), 1 mature male nymph, 15.VIII.2003, 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), 1 mature male nymph and 2 mature female nymphs, 09.IX.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), 3 mature female nymphs, 07.VIII.2004, K. Saito; ditto, 1 mature female nymph, 07.IV.2019, T. Takayanagi; [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), 1 mature female nymph, 13.VIII.2005, 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 female imago, 1 mature male nymph and 3 mature female nymphs, 19.VIII.2020, T. Takayanagi; ditto, 1 mature male nymph and 2 mature female nymph, 25.IX.2020, T. Takayanagi; [16.] Sapporo-shi, Chuo-ku, Kita 1-jo, Higashi 19-chome, Toyohira-gawa Riv., mainstream, 15 m a.s.l. (43°04'04.8"N, 141°23'13.2"E), 2 mature male nymphs, 02.IX.2006, K. Saito; ditto, 1 male imago, 1 female imago, 9 mature male nymphs and 7 mature female nymphs, 21.VIII.2021, T. Takayanagi; KAMIKAWA (outside of the study area): Kamikawa-cho, Souunkyo, Ishikari-gawa Riv., 611 m a.s.l. (43°43'49.2"N, 142°56'34.5"E), 1 male imago, 11.IX.2020, T. Hirose; Horokanai-cho, Shumarinai, Shumarinaigawa Riv., 268 m a.s.l. (44°17'56.0"N, 142°09'31.0"E), 1 male imago, 02.VIII.2020, T. Ito; HIYAMA (outside of the study area): Assabu-cho, Shirooka, Sasamodosawa-gawa Riv., 76 m a.s.l. (41°49'59.0"N, 140°19'57.6"E), 1 female imago, 08.VII.2019, T. Takayanagi.
Nymph (mature, in ethanol), redescription (Figs 15–17).
Body length 10.0–11.0 mm (male), 10.0– 12.5 mm (female). Cercus length ca. body length x 1.2.
Head. Shape trapezoidal. Color dark-brown, with white spots. Compound eyes dark-gray. Ocelli dark gray. Antennae brown (Figs 16a, c). Anterior margin very densely covered with fine medio-dorsally directed hair-like setae extending to lateral margins (Fig. 16b). Dorsal surface covered with fine hair-like setae. Labrum: lateral margins straight and widened anteriorly, anterior margin gently concave, dorsal surface with 8–10 bristles anteromedially and 2 bristles near each side of anterolateral margin. Ventral surface with a row of bristles along lateral margins extending to anterior margins and fine, long hair-like setae medially (Fig. 17a). Mandibles: each outer incisor with three apical teeth and serrated margins, inner incisor with two apical teeth (right mandible) or three apical teeth (left mandible) and serrated sharply on outer margin of both incisors, right inner incisor slender and almost straight. Tuft of long setae on the base of inner incisor of right mandible, tuft of long setae and one comb-like seta on the base of inner incisor of left mandible (Figs 17b, c). Maxillae: one penicillate setae at base of apical tooth complex (Fig. 28c). Hypopharynx: superlinguae distally widened. Lingua shape quadrate. 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. Glossae and paraglossae with long, dense setae.
Thorax. Color dark-brown, with pale markings dorsally (Figs 15a, d). Ventrally white to grayish-white (Figs 15b, e). Pronotum slightly projecting laterally (Fig. 29b). Legs. Each femur with dark brown markings and hypodermal black spot on its middle part of anterior face (Fig. 16d), blade-like long setae on its dorsal edge, short bluntly pointed spines on its ventral edge. Setae on femoral surface variably shaped, most oval to semi-circular (Fig. 17d). Tibia with two dark-brown markings and long hair-like setae on dorsal edge (Fig. 16d). Tarsus darker in proximal area and with long hair-like setae on its dorsal edge (Fig. 16d). Tarsal claw with 3–4 denticles.
Abdomen. Color dark-brown, each tergum with a pair of dark spots (Figs 15a, d). Sterna white to grayish-white (Figs 15b, e). Each tergum with long hair-like setae densely arranged along the midline. Posterior margin of each tergum without long setae and with spines of variable lengths which overlap, forming 2–3 levels (Figs 17j, 31c). Tergum I–VII each with three short postero-lateral projections, ventral and lateral ones blunt and dorsal one pointed and bending upward (Fig. 30c). Posterior margin of sternum IX triangular, with a sharp medial emargination and with long hair-like setae from middle to lateral edges (Figs 17h, i). Dorsal surface of cercus with a row of fine setae.
Gills. Dorsally greyish to brownish, ventrally same (Fig. 16e). Gill I extending anteriorly and meeting beneath mesothorax (Figs 15b, e, 17e). Posterior tip of Gill VII slightly expanded beneath sternum. Rounded projections at costal-proximal margin of gill plates II–VII (Figs 17f, g). Costal margin with rough surface. Each gill plate with filaments forming a fan-shape together. Gill VII with longitudinal fold (Fig. 17g).
Male imago (in ethanol), redescription (Fig. 18).
Body length 12.6 mm. Cercus length ca. body length x 2.5. Forewing length 14.5 mm.
Head. Yellowish-white. Frons margin with brown border. Frons shape relatively round. Compound eyes dark-gray to black. Ocelli grayish-white with dark-gray border.
Thorax. Ground color orange to brick-color, internal tissues visible. Pronotum without markings. Mesonotum without markings, darker in scutellum. Mesopleuron with dark markings. Metanotum dark on scutellum (Fig. 18a).
Wings. Hyaline, veins white. Pterostigmatic area cloudy. Forewing with black markings on costal brace to the base of radius and media (Fig. 18e). Hindwing with black markings on the same part as forewing. Legs. Each femur with a black spot on the middle part. Fore tibia dark at the tip. Each segment of fore tarsus becoming shorter distally and each joint color dark. Fourth segment shortest on mid and hind tarsus, each joint color dark (Figs 18b–d). Tarsal claws dissimilar, one hooked-shape and the other oblong.
Abdomen. Ground color brownish-white to transparent, posterior margins of segments I–IX with dark-brown streaks. Segment VIII–X yellowish white, internal organs and tissues visible (Fig. 18a). Posterior margin of styliger plate bulging, tip rounded. Projection on forceps base not developed. Forceps four segmented, distal two segments color dark. Penis lobes without spines, with complex concavity, titillators developed (Fig. 18f). Cercus white, basally brown.
Female (in ethanol), redescription (Fig. 19).
Body length 11.9 mm. Cercus length ca. body length x 2.4. Forewing length 13.5 mm.
Head. Yellowish-white. Frons triangular. Compound eyes dark-gray to black, grayish-green when alive.
Thorax. Coloration as in male imago (Fig. 19a). Wings. Veins dark.Markings as in male imago. Legs. Coloration and markings as in male imago. Fore tarsus not elongated. Fourth segment shortest on each tarsus, other segments almost equal length (Figs 19b–d). Tarsal claws dissimilar as in male imago.
Abdomen. Coloration and markings as in male imago. Reddish eggs visible when alive (Fig. 19a). Posterior margin of subgenital plate quadrate, apices rounded. Posterior margin of sternum IX with medial emargination (Fig. 19e).
Diagnosis and comparison. Nymph. This species is easily distinguished from other species in the study area by 1) a strongly extended gill I (Figs 15b, e, 17e) and 2) a prominent dorsal projection of the postero-lateral projections located on each abdominal tergum (Fig. 30c). Male imago. This species has black markings at the base of the forewing and has titillators on its penis, similar to E. L-nigrum, but its styliger plate is rounded, and the projection at the base of the forceps is less developed in contrast to E. L-nigrum.
Remarks. Nymph. The specimens identified here as E. curvatulus agree with the description of Iron sp.? (Uéno 1928) which supports Imanishi (1934). Male imago. The specimens identified here as E. curvatulus agree with the original description and holotype (Matsumura 1931). Subgenus attribution. Kluge (2004) attributed this species to the subgenus Iron, but it should be placed in the subgenus Caucasiron due to the following characteristics: 1) hairs on the anterior margin of the head are directed dorsomedially (nymphs, Fig. 16b); 2) each of gills II–VII has a well-developed projection (nymphs, Figs 16e, 17f, g); and 3) gill plates form a “suction disc” (nymphs, Figs 15b, e). Additionally, the male imago of this species lacks latero-dorsal spines on its penis lobes.
This species was originally described based on male imaginal specimens collected from the Tama-gawa River in Tokyo, Honshu (Matsumura 1931; 1932). The holotype is preserved at SEHU, and male imagines of this species can be confidently identified by comparison with the type specimen (Fig. 34). Nymphs of this species were identified using DNA barcoding, and their morphological characteristics matched those of Uéno's Iron sp.? (Uéno 1928). Although Imanishi (1934) associated Uéno's Iron sp.? with E. uenoi, the male genital structures of the type specimens of E. curvatulus (Fig. 34e) and E. uenoi (Fig. 32d) are markedly different, making this identification highly questionable. Ishiwata (2001a; 2001b; 2018) suggested there may be misidentifications in Imanishi's series of works.
Emergence period and habitat. Fully mature nymphs and imagines were obtained from July to October. This species was collected from a wide area within the Toyohira-gawa River system.
Distribution. Japan (Hokkaido, Honshu, Shikoku, and Kyushu).
description: Published as part of Takayanagi, Tatsushi & Yoshizawa, Kazunori, 2025, Taxonomic review of Epeorus s. l. Eaton, 1881 (Ephemeroptera: Heptageniidae) in Sapporo City and adjacent areas, Hokkaido, Japan, pp. 1-49 in Zootaxa 5594 (1) on pages 21-27, DOI: 10.11646/zootaxa.5594.1.1, http://zenodo.org/record/14953985