Ephemera (Sinephemera) japonica 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 : 387-392

Ephemera (Sinephemera) japonica McLachlan, 1875

Figures 24–30

Material examined. Russia: Sakhalinskaya Oblast: Sakhalin Island, Belaya River , 2 km southeast of “Sokol” station, 21.07.2001, 1♀ adult, V. Teslenko; Sakhalin Island, unnamed stream, 25 km south of Vostochny village , 01.08.2001, 1♀ adult, V.Teslenko; Iturup Island , Ketoviy Bay , Podoshevka River , 1.5 km above Fish Hatchery, 29.07.1997, 4♀ adults, V. Teslenko; Kunashir Island , Lesnaya River , about 1 km above the mouth of Kislyy Stream, 04.08.1994, 2♀ adults, T. Tiunova .

Distribution. Far East Russia, Japan, China.

The egg was described previously by Koss & Edmunds (1974) and Tojo & Machida (1998, p. 574: fig. 1). The description notes: the shape of the egg is ellipsoidal, about 200x100 µm; the adhesive layer is very thin (about 0.1 µm); the surface of the chorion has an ill-developed reticulation (by Tojo & Machida 1998) or smooth (by Koss & Edmunds 1974); micropyle, one per egg; the sperm guide is undeveloped; micropylar canal according to Koss and Edmunds (elongated, 42–55 µm long); according to Tojo and Machida (about 20 µm).

According to our data, the egg is oval, more often ovoid in shape ( Figs 24–25 , 27–28 ). Dimensions: 293.0– 334.0 µm in length (315.4 µm) and 173–197 µm in width (180.1 µm). The extrachorion-adhesive layer covering the egg is thin, smoothly amorphous ( Fig. 24–25 ). In the equatorial area, there is one micropyle per egg ( Fig. 27 ). The micropyle is of the “tagenoform type,” with a sharply expanding, rounded, poorly defined sperm guide, 14–16 μm long and 21–24 μm wide ( Figs 27, 29 ). As in other species, the sperm guide is visible only on the adhesive surface of the egg. After the removal of the adhesive layer, only the micropylar canal is visible ( Figs 28, 30 ). The micropylar canal is 16–30 μm long and 3–8 μm wide, protruding prominently above the adhesive layer and chorion ( Figs 29–30 ). The surface of the chorion is smooth ( Fig. 28 ), or with a weakly expressed very fine reticulation, and the proximal part of the tunnel-type micropylar canal and a micropylar opening 2–3 μm wide are clearly visible on the surface of the chorion ( Figs 28, 30 ).

Figures

FIGURES 24–26. Egg morphology of Ephemera (Sinephemera) japonica: 24–25, remains of the adhesive layer on the egg surface; 26, chorion thickness. AL-Ex—complex adhesive-extrachorion layer; AL—adhesive layer; C—chorion.

FIGURES 27–30. Egg morphology of Ephemera (Sinephemera) japonica: 27–28, egg shapes; 29, micropyle in the complex extrachorion-adhesive layer; 30, proximal part of micropylar canal on chorion surface. AL—adhesive layer; CM—canal micropylar; MO—micropylar opening; CS—chorion surface; mp—micropyle; SG—sperm guide.