Isoperla eximia Zapekina-Dulkeit 1975

Isoperla eximia Zapekina-Dulkeit, 1975 Figs. 18–27 Material examined. Russia, Far East, Khabarovsk Krai: 1♂, Bol’shaya Uda River, 18.08.2021, N. Yavorskaya; 1 L, Bol’shaya Del’ya River, 11.07.2022, coll. I. Tiunov; 1♂, Bol’shaya Del’ya River, 12.08.2022, coll. I. Tiunov; 1♂, Malaya Del’ya River, downstream, 5.08.2022, coll. I. Tiunov; Jewish Autonomous Region: 1 L, Nature Reserve Bastak, Bol’shoy Sorennak River, near the bridge to the Kukan, 11.07.2018, coll. T. Vshivkova; 1♂ 1♀, Kuldur River, Kuldur settlement, above the spring, Amur R. basin, 17.08.2024, coll. N. Yavorskaya; 2♀, Bastak Nature Reserve, Bastak River, Amur R. basin, 14.08.2024, coll. N. Yavorskaya. Japan, Hokkaido: 1♂ 1♀ 5 L, Tobetsu River, 43°28.67 N 144°17.65 E, 10.09.1995, coll. G. Kraft; 1♀, Shiretoko Pass Summmit, near Rausu, 44°3.2 N 145°6.2 E, 11.09.1995, coll. G. Kraft; 2♀, Soukippkaononai River near Shibetsu town, 43°44.4 N 144°53.6 E, 12.09.1995, coll. G. Kraft; 9♀, trib. Churui River, at bridge near Shibetsu town, 44°43.7 N 144°48.4 E, 12.09.1995, coll. G. Kraft; 1♀, 1 L, trib. Ikushina River, near Shibetsu town, 43°48.1 N 144°46.9 E, 12.09.1995, coll. G. Kraft. Egg. Shape oval; marginally asymmetrical, anterior pole is rounded more widely than posterior pole (Fig. 18), and a concave cross-section (Fig. 20). Length 345–349 µm, width at equator 222–227 µm (n=2). Collar well developed, with irregular longitudinal ridges and a flanged and incised rim; base of collar surrounded by a wide smooth shoulder limited by a ring (Figs. 19–20). Anchor mushroom-shaped, with small grouped globular bodies covering the entire surface of anchor evenly (Figs. 18–19). Follicle cell impressions near the collar ranged from subrectangular to hexagonal (Figs. 18, 20). Chorion covered with hexagonal FCIs with thick elevated ridges (Figs. 18, 21‒23); floors with numerous (ca. 37–39) very shallow and small pits (Figs. 22‒23). Micropylar row well visible along anterior ⅓ (Figs. 18, 21). Micropyles located near paired ridges and surrounded with rosettes of FCIs (Figs. 18, 21, 23). Micropylar canals straight, tunnel-shaped, and relatively long; orifices set in small oval cup-like depressions with long, smooth, slanted, and open sperm guides extending from cup rims (Figs. 18, 21, 23). Remarks. The egg of I. eximia is described here for the first time. Eggs from Japan (Figs. 24–27) and the Russian Far East are similar in size (330–357 µm long, 177–207 µm wide, n=4), have a collar with a smooth shoulder at the base, limited by a raised ring (Fig. 25), and have a similar chorion structure (Figs. 26–27). The main difference between Japanese eggs is their oblong shape (Figs. 18, 24). It is possible that the shape and appearance of eggs from the Japanese population vary depending on the degree of hydration. Eggs from dried Japanese females appear almost parallel-sided and narrow. Distribution. East Palaearctic. Russia, Siberia: Altai, Sayan, Transbaikalia; Far East: Southern Yakutia, Amurskaya Oblast, Jewish Autonomous Region, Khabarovsk Region, Primorsky Krai, Sakhalin, and South Kuril Isles. East Kazakhstan (Devyatkov 2022). Mongolia. China (Changbai Mountain and Jilin Province) (Wang et al. 2018, Chen et al. 2019). Isoperla eximia is recorded from Japan (Hokkaido) for the first time.