A new species of Hemicorallium (Anthozoa, Octocorallia, Coralliidae), along with a revised identification key to species of the genus.

A new precious coral species, Hemicorallium osmanthogemmum sp. nov. (Scleralcyonacea, Coralliidae), retrieved from a depth of 550 m in Kochi Prefecture, Japan, is described, and an updated identification key for the genus Hemicorallium is provided. The new species is confirmed as belonging to the genus Hemicorallium based on the presence of nonretractile but contractile autozooids with an ovate-cylindrical shape and sclerites comprising elongated rods, 6-8-radiates and double clubs, with elongated rods present exclusively in the tentacles. Moreover, the species is distinct from all its congeners in that it has orange coenenchyme and a pink axis, with autozooids distributed only on the front side of the branch, forming clusters at the branch tips. These morphological features differ from those of all previously described species of Hemicorallium, and molecular analysis of mitochondrial sequences (16S, ND1, ND2, ND3, ND6, COI, MSH, and IGR1) further corroborates the validity of this new species. This is the first report of Hemicorallium off the coast of Kochi Prefecture, Japan.