Ephemera orientalis McLachlan 1875

Ephemera orientalis McLachlan, 1875 (Figs. 1A, 1B, 1C, 2A, 2C, 2E, 3A, 3B, 4A, 4E, 4I, 5A) Ephemera orientalis McLachlan, 1875: 167; Demoulin, 1965: 215; Tshernova, 1973: 225; Gose, 1981: 13; Bae et al., 1994: 70; Bae and Yoon, 1997: 148; Hwang et al., 2003: 430. Material examined. South Korea: Seoul: 6 males & 23 female subimagoes, Gwangnaru, Hangang (R.), 2018- V-14, Park SH, Seok SW. Gyeonggi-do: 10 male subimagoes & 19 female subimagoes, Gapyeong, 2011-V-2; 4 males & 13 female subimagoes, Gapyeong, 2011-VI-2; 17 males & 23 females, Gapyeong, Yeopgwang-gyo (Br.), 2017-V-8; 16 males & 19 females, Namyangju-si, Deokso, 2018-V-13; 12 males & 20 females, Pocheon-si, Hwanhyunmeon, 1991-VII-18; 3 males & 14 females, Yangpyeong, 2002-IV-29. Gangwon-do: 25 males & 37 females, Jeongsun-gun, Hwaam-myeon, 2018-V-7, Park SH, Kim JS; 5 larvae, Jeongseon, 2018-VI-2, Park SH, Kim JS; 4 larvae, Jeongseon-gun, Bungyang-ri (E 128°40 ʹ 02.11 ʺ N 37°22 ʹ 41.04 ʺ), 2018-IX-14, Park SH, Kim JS, Mayorga A; 6 larvae, Wonju-si, Cheondungsan (Mt.) (E 127°56 ʹ 52.88 ʺ N 37°04 ʹ 31.31 ʺ), 2016-IX-11, Park SH, Seok SW. Gyeongsangnam-do: 9 larvae, Sancheong-gun, Jirisan National Park, 2017-V-31, Bae YJ, Park SH. Diagnosis. Body length 16.4± 0.3 mm in female adult and 14.1± 0.1 mm in male adult (Fig. 1A, 1B). Pronotum with lateral dark stripes and yellowish pale median band (Fig. 2A, 2D, 2E). Abdomen with paired multi-striped markings; segments I- II of abdominal tergum with dark pigment covering all or almost all the segments; pigmentation can be as dots, bars or irregular-shaped (Figs. 3A, 3B, 4A). Adult. Forewing transparent with dark brown marks on crossveins; costal area dark brown; MP1-MP2 with a dark spot; CuA and MP2 fused (Fig. 1C). Forelegs anterior half of fore femur pale brown and posterior half dark brown; fore tibia and tarsus dark brown (Fig. 1A). Male genital lobes square-shaped, sclerotized and without prominent apical inner concavity; penis with distinct titillators triangular-shaped (Fig. 5A). Mature larva. Claw pointed and elongated (Fig. 4I). Posterior margin of tergum X trapezoid-shaped and pronounced (Fig. 4E). Distribution. China, Japan [type locality], Korea, Mongolia, Russia. Remarks. Among the Ephemera species with paired multi-striped markings on abdominal segments, this species is one of the most widely distributed species in Far East Asia, and is well studied especially in Japan and South Korea in terms of life history (Gose, 1970; Lee et al., 1995; 1999; 2008; Hwang et al., 2009; Lee et al., 2011; Seok et al., 2019), the level of genetic diversity and its ecology (Kuroda et al., 1984; Lee et al., 1995; Kang et al., 2005; Hwang et al., 2009; Takenaka et al., 2023). This species was redescribed based on the holotype (Demoulin, 1965), although the redescription lacked details of larva and male genitalia. Because of its wide distribution in a variety of habitats and geographical regions, morphological variations between local populations or cohorts are still poorly understood. Based on a close examination of adult and larval materials, we found that the shape of the pigmentation on the abdominal segment I- II (Fig. 3A, 3B; also illustrated by Gose, 1981) could be a useful character to distinguish E. orientalis from its sympatric E. sachalinensis. In addition, despite its wide distribution across various habitats and countries, studies on the morphological variability among populations and cohorts remain incomplete. For instance, this study observed some morphological variations. Specimens from different sites in South Korea exhibited certain variations in the pigmentation patterns on tergal segments I- II (Fig. 3A, 3B), such as complete dark pigmentation, or incomplete dark pigmentation (Fig. 3A). However, other distinctive morphological features proposed in this study remained consistent across sex, both larval and adult stages.