Ephemera sachalinensis Matsumura, 1911

Ephemera sachalinensis Matsumura, 1911 View in CoL ( Figs. 1D, View Fig

1E, 1F, 2B, 2D, 2F, 3C View Fig , 4B, 4F, 4J View Fig , 5B View Fig , 6)

Ephemera sachalinensis Matsumura, 1911: 7 View in CoL ; Tshernova, 1973: 329; Hwang et al., 2003: 430.

Lectotype (New designation). Female subimago (pinned; Fig. 6A), カṽ]ト (Karafuto = Sakhalin), Ξϊ (Miyake: Collector’s name), Matsum (= Matsumura); ZfflVƜ - 7/1907, deposited at the Hokkaido University Museum, Sapporo, Japan.

Other material examined. South Korea: Seoul: 34 female subimagoes, Amsa-dong, Hangang ( R.), 2017- VI-1, Kang JH, Seok SW, Lim CS ; 1 male imago & 14 female subimagoes, Seoul, Gwangnaru, Hangang ( R.), 2018-V-14, Park SH, Seok SW . Gyeonggi-do: 1 male, Namyangju-si , Gu-am-dong-san, 1994-VII-20, Bae YJ ; 3 male imagoes, Gapyeong , 2005-VIII-21 ; 12 female imagoes, Namyangju-si, Deokso , 2017-VI-29, Kang JH, Park SH, Lim CS ; 4 larvae, Gapyeong , 1997-V-30, Bae YJ ; 5 male subimagoes & 12 female subimagoes, Gapyeong , 2017-V-8 ; 8 male subimagoes, Gapyeong , 2017- V-20, Park SH, Uy CJ. Gangwon-do : 3 larvae, Jeongseon-gun, Jeongseon-eup (E 128°42 ʹ 50.5 ʺ N 37°23 ʹ 15.3 ʺ), 2018-VI-2, Park SH, Kim JS GoogleMaps ; 37 larvae, Jeongseon-gun, Hwaam-myeon , 2018-VI-2, 2018-V-7, Park SH, Kim J . Jeollanam-do: 2 male subimagoes & 3 female subimagoes, Yeongam-gun, Hoemun-ri (N 34°46 ʹ 46.1 ʺ E 126°40 ʹ 47.6 ʺ), 2018-VII-18, Mayorga A, Uy CJ, Jung SW GoogleMaps . North Korea: 1 male imago, Hwanghae Province (= Hwanghae-do): Haeju , 1986-VI-8, Kwang S . Mongolia: 3 female imagoes, Bulgan Aimag, Teshing Soum (wetland), 4.3 km SSW of Teshing (N 49°90 ʹ 72.5 ʺ E 102°65 ʹ 66.5 ʺ), 970 m a.s.l., 2005-VII-10-11, Samaa . Russia: 1 male imago, Primosky Krai, Nakhodka City, Westshore of Rivadia Lake (N 42°51 ʹ 46.43 ʺ E 103°38 ʹ 53.44 ʺ), 2013-VIII-17, Bae YJ, Kang JM, Lee JM, Vshivkova T GoogleMaps .

Redescription (adult female lectotype). Specimen is pinned. Overall body yellowish and brownish ( Fig. 6B). Pronotum with two lateral dark stripes becoming narrower basally and a yellowish pale median band ( Fig. 6D). Mesonotum with a thick dark median band and lateral borders with dark pigmentation ( Fig. 6C). Abdomen with paired multi-striped markings; abdominal terga I- II pale without dark pigmentation; terga III- VI with apparently dark multiple stripes but becoming unclear at last segments ( Fig. 6C, 6B). Forewings and hindwings completely damaged ( Fig. 6B). Three yellowish to brownish caudal filaments present. Forelegs broken; middle legs and hind legs completely yellowish ( Fig. 6B).

Diagnosis. Body length 21.80± 0.50 mm in female adult and 18.50± 0.10 in male adult ( Fig. 1D, 1E View Fig ). Pronotum with lateral dark stripes becoming narrower basally and a yellowish median band ( Fig. 2B, 2D, 2F). Abdominal terga I- II pale without dark pigmentation ( Fig. 3C View Fig ).

Adult. Forewings with dark brown marks on crossveins; costal area dark brown; CuA and MP2 fused ( Fig. 1C View Fig ). Foreleg trochanter, tibia-femur, tibia-tarsus junctions with dark pigmentation ( Fig. 1D View Fig ). Male genital lobes non-sclerotized, rounded at apex and elongated with inner concavity; penis with distinct thin titillators ( Fig. 5B View Fig ).

Mature larva. Claw neither elongated nor sharp ( Fig. 4J View Fig ). Posterior margin of tergum X trapezoid-shaped and not pronounced, almost straight ( Fig. 4F View Fig ).

Distribution. China, Kazakhstan, Korea, Mongolia, Russia Far East [type locality].

Remarks. This species has not been well defined in terms of taxonomy and relations with other sympatric species in the same genus. Because the type information was lacked in the Matsumura’s (1911) original description of this species, mayfly taxonomists like Tshernova (1973) were unable to locate any type specimens that were used in Matsumura’s original description of this species. While the first author of this study had searched Matsumura’s collection in the Hokkaido University Museum in Sapporo, a female subimago specimen ( Fig. 6A) that was most probably labeled and used by Matsumura in the original description of Ephemera sachalinensis Matsumura, 1911 was found. The locality (Karafuto = Sakhalin) and collector (Miyake) also coincide with the information in the Matsumura’s brief description of the species: “Fundorte: Chippsani und Suzuya, gesammelt in 2 females. Exemplaren von Herrn B. Miyake [= Locations: Chippsani and Suzuya, collected in 2 females. Specimens by Mr. B. Miyake]” ( Fig. 6A). Although the condition of this Matsumura’s specimen is not complete, some preserved characters such as the lateral dark stripes becoming narrower basally from pronotum and the lack of pigmentation at the abdominal terga I and II ( Fig. 6B) well substantiate Matsumura’s (1911) species concept of E. sachalinensis . The lectotype designation must involve one of the original specimens used by the author for the description, which is the case in our study. Further revision of fresh specimens from the type locality (Sakhalin, Russia) will be beneficial to complement both Matsumura’s original description (1911) and ours. The discovery of this historical specimen has significant scientific and historical relevance.

A B 5 mm C D Lateral Dark StripeS beCOming narrOWer baSally

Ephemera sachalinensis is morphologically similar to E. pieli Navás based on the observation data of Chinese specimens provided by Li et al. (2023). Both E. sachalinensis and E. pieli lack dark pigmentation on the abdominal terga I- II, but E. pieli possesses two lateral dark spots on the abdominal tergum II. In addition, E. sachalinensis can be distinguished by different shape of male genitalia ( Li et al., 2023).

Ephemera sachalinensis is widely distributed in Northeast Asia and largely overlaps in distribution with its sympatric E. orientalis ( Tshernova, 1973; Bae and Sóldan, 1997; Hwang et al., 2003; 2008). Further investigations on life history, distribution and habitat, and other ecological features are needed to understand adaptation and evolution of these two closely related species. Compared to E. orientalis , in specimens from different sites around South Korea and other countries, it was not found important variability in the diagnostic characters for this species.