A revision of the genus Calcigorgia (Cnidaria, Octocorallia, Acanthogorgiidae) with the description of three new species.

Octocorals of the Acanthogorgiid genus Calcigorgia have been examined, from Japan, Sea of Okhotsk, and Bering Sea. The four known species are re-described and scanning electron microscopy (SEM) images of sclerites presented. Three other species are described and depicted, bringing the total number of Calcigorgia species to seven. Calcigorgia simushiri, Dautova 2018 is synonymized with C. spiculifera Broch, 1935. A neotype for C. spiculifera has been designated.

The genus Bebryce (Cnidaria, Octocorallia, Plexauridae) at Japan, with descriptions of three new species.

Three new deep-water species of Bebryce from Japan are described and depicted using Scanning Electron Microscopy: Bebryce otsuchiensis sp. n., Bebryce rotunda sp. n., and Bebryce satsumaensis sp. n. Bebryce studeri Whitelegge, 1897, was reported from Japanese waters for the first time, bringing the total of Japanese Bebryce species to six. Five of these six species seem to be endemic to Japanese waters and all occur in deep water up to 213 m. A key to the Bebryce species is presented.

Species of Elasmogorgia and Euplexaura (Cnidaria, Octocorallia) from Japan with a discussion about the genus Filigella.

Octocorals with thread-like colony shape have been re-examined, mainly from Japanese waters. The holotypes of Elasmogorgia filiformis and Filigella boninensis and a syntype of Filigella mitsukurii have been studied. Euplexaura arbuscula is identified and Euplexaura yayoii sp. n. described.

Melithaeidae of Japan (Octocorallia, Alcyonacea) re-examined with descriptions of 11 new species.

Japanese melithaeid type material is re-examined and re-described. The sclerites of the different species are depicted using Scanning Electron Microscopy. All Japanese species of the family Melithaeidae treated here belong to the genus Melithaea and are endemic to Japanese waters. Old museum material and newly collected specimens from Japanese waters are identified after comparison with this type material. Acabaria modesta var. abyssicola is regarded a separate species, here named Melithaea abyssicola (Kükenthal, 1909). In addition, 11 new species are described: Melithaea boninensis sp. n., Melithaea doederleini sp. n., Melithaea isonoi sp. n., Melithaea keramaensis sp. n., Melithaea oyeni sp. n., Melithaea ryukyukensis sp. n., Melithaea sagamiensis sp. n., Melithaea satsumaensis sp. n., Melithaea suensoni sp. n., Melithaea tanseii sp. n., and Melithaea tokaraensis sp. n.. Pleurocorallium confusum Moroff, 1902, Pleurocoralloides formosum Moroff, 1902, Melitodes flabellifera Kükenthal, 1908, and Melitodes densa Kükenthal, 1908 are synonymized with Melithaea japonica (Verrill, 1865). We have designated a neotype for Melithaea mutsu Minobe, 1929. A key to the Japanese melithaeids is presented.