The Eudorella hwanghaensis group

Eudorella hwanghaensis Hong & Park, 1999, E. ryukyuensis Akiyama & Gamô, 2005, E. bathyhwanghaensis sp. nov., and E. suluensis sp. nov. are closely related species sharing the following characters of females. (1) Antenna 2 has plumose setae on the inferior margin. (2) The basis of maxilliped 2 has a group of setae on its inner margin. (3) The basis of pereopod 1 has 1–3 robust spiniform setae on its ventral surface. (4) The frontal margin of the carapace is serrated, (5) The propodus of pereopod 2 has a deep notch on the distal corner, reaching close to the basal end of the article. (6) The 1st article of the uropod endopod is 4 times or longer than the 2nd article.

All these species are distributed in the vicinity of southern Japan, but the depth of the habitat of the Japanese species differ: 59–596 m in E. hwanghaensis; 576–1056 m in E. bathyhwanghaensis; and 703–1533 m in E. ryukyuensis . The shape of pereopod 3 in the adult males may be an common evolutionary trait of the E. hwanghaensis group. In E. ryukyuensis, this appendage is normal for the genus (Akiyama & Gamô 2005). The distal three articles of this appendage in E. bathyhwanghaensis show a secondary sexual character: a chela-like form. On the carpus, 1 seta on the distal end is unusually robust and curved, and the other four setae are normal for the genus (Fig. 12I). In E. hwanghaensis, adult males show a more specialized morphology of this article: two setae on the distal corner are robust and curved, and the other three setae unusually stiff and long (Fig. 26 B). Considering the specialization pattern of these three species, the ancestors of the E. hwanghaensis group probably would have migrated from the bathyal zone to shallower water, developing more specialized male sexual characters. Eudorella suluensis is distinguished from the three Japanese species by the presence of tubercles on the upper front corner of carapace, which is unique for the genus.

Eudorella emarginata (Kröyer, 1846) shares some morphological characters with the E. hwanghaensis group, especially, (1) antenna 2 with 2–3 setae on the lower margin, and (2) the basis of pereopod 1 with 1–2 spiniform setae on the ventral surface. These characters were not observed in the other members of Japanese Eudorella . Although geographical distribution and morphology of the basis of maxilliped 2 of E. emarginata are different, this species may be related to the E. hwanghaensis group.