Ephemera (Ephemera) orientalis McLachlan, 1875

Tiunova, Tatiana M., 2024, Egg morphology of six East Palaearctic species of the genus Ephemera Linnaeus (Ephemeroptera: Ephemeridae), Zootaxa 5497 (3), pp. 381-399 : 382

Ephemera (Ephemera) orientalis McLachlan, 1875

Figures 1–8

Material examined. Russia: Primorsky Krai, Ussuri River basin, Kabarga River , below the road bridge, Vladivostok – Khabarovsk highway, 17.06.2000, 3♀ adults, T. Tiunova; Ussuri River, near Stepanovka village , 15.06.2005, 2♀ adults, T. Tiunova ; Khabarovsky Krai, Amur River, near Bystrinsk village , 30.06.2005, 1♀ adult, T. Tiunova .

Distribution. Siberia, Far-East Russia, Japan, Mongolia, Korea, N.E. China, Kazakhstan (Irtysh River basin).

The egg has been described by Okazaki (1981, p. 9: fig. 5; 1984, p. 21: fig. 16), Su & Zhu (1997, p. 122: fig. 70), and Tojo & Machida (1998, p. 576: fig. 3). From the above descriptions, the following can be emphasized: the egg is rectangular in shape, with a length of 187.0 µm and a width of 120.8 µm. In the work of Tojo and Machida, the egg is ellipsoidal in shape, about 200x100 µm, the adhesive layer is thick (3–4 µm), smooth, the chorion has well-defined reticulation, the opening diameter is 1–1.5 µm, and the sperm guide is hood-like in shape.

According to our data, the egg has an oval shape close to quadrangular with rounded corners ( Figs 1–2 ). Dimensions: 173.0–206.0 µm in length (191.3 µm) and 104.1–123.4 µm in width (111.0 µm). The attachment structure is a complex extrachorion-adhesive layer (AL-Ex) that covers the entire surface of the chorion (CS) ( Figs 1–2 , 5–6 ). Its thickness for E. orientalis is 1.6 –1.8 µm ( Fig. 8 ). The surface of the adhesive layer (AL) is slightly bumpy ( Figs 1–2 ). There are one or two micropyles (mp) per egg in the equatorial area ( Figs 1–2 , 5–6 ). The micropyles are “tagenoform-type,” with a well-expressed sperm guide (SG) oval and relatively deep ( Figs 3–4 ). Sperm guide is 5.8–10.4 µm long and 5.0–6.1 µm wide. It should be noted that the sperm guide is only clearly visible on the adhesive surface of the egg. Once the adhesive layer has been removed, the sperm guide is not visible on the chorion ( Figs 3, 4 , 6 ). The micropylar canal, 12–18 µm long and 4–6 µm wide, protrudes slightly above the adhesive layer ( Figs 2–3 , 5 ). As shown previously ( Ubero-Pascal & Puig 2007), features of the chorion structure are visible on SEM only after removal of the adhesive layer. For E. orientalis , the surface of the chorion is finely wrinkled ( Figs 5–6 ). The thickened proximal part of the tunnel-type micropylar canal and micropylar opening are clearly visible on the surface of the chorion. ( Figs 6–7 ).

Figures

FIGURES 1–4. Egg morphology of Ephemera (Ephemera) orientalis: 1–2, general shape; 3–4, micropyle of the complex extrachorion-adhesive layer. CM—canal micropylar; MO—micropylar opening; mp—micropyle; SG—sperm guide.

FIGURES 5–8. Egg morphology of Ephemera (Ephemera) orientalis: 5–6, egg surface without complex extrachorion-adhesive layer; 7, proximal part of micropylar canal on chorion surface; 8, thickness of the layer forming the eggshell. AL-Ex—complex adhesive-extrachorion layer; CS—chorion surface; MO—micropylar opening; mp—micropyle.