Xanthoneuria unimaculata (Zhiltzova, 1981)

Figs. 1–7

Material examined. Russia, Far East, Jewish Avtonomnaya Oblast: 2♀, Kuldur River ( Bira R. basin, Amur R. basin), 2 km below Dvurechye village, 19.08.2003, coll. T. Tiunova; 3♀, Kuldur River, 4 km below Dvurechye village, 18.07.2005, coll. T. Tiunova; 5♀, Bira River, Amur River basin, Razdolnoye village, 4.08.2005, coll. T. Tiunova; Primorsky Krai: 1♀, an unnamed stream near the fish factory, Barabashevka River basin, 26.08.2002, coll. T. Tiunova.

Egg. Ovoid (Figs. 1–2), beige, length of 364–396 µm, and width at the equator of 260–285 µm (n=9). Egg is 1/4–1/2 its length covered with a large, thin, and cap-like anchor with a low star-shaped collar attachment to the chorion tightly (Figs. 1−3, 6−7). The globular bodies on the anchor surface are small and concentrated into longitudinally elongated groups of a vaguely hexagonal shape, located in a peripheral area along the anchor edge, and form a circular band whose length does not exceed 1/3 of the anchor length (Figs. 1, 6−7); the top of the anchor has an unmodified surface (Figs. 1, 6−7). The chorion has minute punctures inside the shallow hexagonal follicle cell impressions, faintly visible in the anterior and posterior poles; in the equatorial region, the chorion surface appears smooth (Figs. 6−7). A row of micropyles is located behind the equator, closer to the anterior pole (Figs. 1−6). Micropylar canals are tunnel-shaped, straight, and relatively long; orifices are raised slightly and surrounded by an oval sperm guide (Figs. 4−5).

Comments. The X. unimaculata egg is similar to the X. fulva (Klapálek, 1907) egg from Japan (Honshu) in shape appearance and cap-like anchor covering 1/2 of the egg, in the circular distribution of globular bodies in the peripheral anchor area, in chorion structure with minute punctures and shallow hexagonal follicle cell impressions, and in the shape of micropylar canals (Isobe 1997, Uchida et al. 2011). The more conspicuous details of the chorion structures in X. fulva as well as X. jouklii (Klapálek, 1907) were not observed (Isobe 1997). The only difference with X. unimaculata is the presence of a low stellate collar attachment to the chorion tightly. Eggs of Xanthoneuria (Uchida et al. 2011) are thought to lack a collar, although a similar structure has been identified in X. fulva and referred to as an “anchor attachment” (Isobe 1997).

Distribution. East Asian mainland species with distribution limited by the Russian Far East (south of Amurskaya Oblast, Jewish Avtonomnaya Oblast, and south of Primorsky Krai). Xanthoneuria unimaculata has been reported also from Korea without any detailed locality (Uchida 1990, Uchida et al. 2011) and North Korea (Murányi et al. 2016).