Egg morphology of six East Palaearctic species of the genus Ephemera Linnaeus (Ephemeroptera: Ephemeridae) Author Tiunova, Tatiana M. text Zootaxa 2024 2024-08-26 5497 3 381 399 http://dx.doi.org/10.11646/zootaxa.5497.3.4 journal article 10.11646/zootaxa.5497.3.4 1175-5326 13618713 BFEC2071-EFCF-4489-93AD-18F3B0DCDBC6 Ephemera ( Ephemera ) transbajkalica Tshernova, 1973 Figures 16–23 Material examined . Russia : Amur Oblast , Selemdzha River basin, Burunda River , mouth, tributary of Nora River , 16.06.2004 , 2♀ adults, T . Tiunova; Republic of Sakha (Yakutia), Aldan River basin, Ungra River , base of Ungrinsky reserve “Yukhta,” 01.08.2006 , 2♀ adults (reared), T . Tiunova . Distribution. East Siberia, Far East Russia , Mongolia . The egg is oval-shaped ( Figs 16–17 ). Dimensions: 220.0–226.0 µm in length (220.8 µm) and 123.0–129.0 µm in width (124.6 µm). The thickness of the extrachorion-adhesive layer is 1.3–1.7 µm ( Figs 21, 23 ). The surface of the adhesive layer is slightly roughened; almost smooth ( Figs 16, 18 ). There are one or two micropyles in the equatorial area ( Figs16–17 ); micropyles are “tagenoform-type”; sperm guide well expressed (10.0–19.6 µm long, 4.2–7.2 µm wide), elongated, oval, with pointed distal margin, not deep ( Figs 18–19 ). Micropylar canal: 4.0–6.0 µm long and 2.3–7.1 µm wide; weakly protrudes above the adhesive layer ( Figs 16, 18 ). The chorionic surface is covered by the regular mesh unit’s penta- or hexagonal cells, each with a flat, almost smooth bottom and a convex protuberance in the middle ( Fig. 23 ). The proximal part of the micropylar opening elevates above the chorion ( Figs 20, 22 ).