Two new paralcyoniid octocorals from Japan (Anthozoa: Alcyonacea).

Two new species of paralcyoniid octocorals are described from Japan. One of them, Ceeceenus retractus n. sp., is the fifth species of the genus, and the other, Nanalcyon sagamiense n. gen. n. sp., is proposed as a new genus. Nanalcyon is similar to the Mediterranean and Atlantic genera Maasella Poche, 1914 and Paralcyonium Milne Edwards and Haime, 1850, but the new genus clearly differs from these in having independent colonies not joined by stolons. The ultrastructure of the sclerites is compared among the new genus, Ceeceenus and Paralcyonium by means of SEM. All three genera display the same three main types of sclerites, flat platelets, rods and spindles, the ultrastructure of all consisting of non-branching fibrous crystals. In addition to these, two genera, Ceeceenus and Paralcyonium, have flat oval platelets with the ultrastructure showing branching dendritic crystals, lacking in Nanalcyon.