The Syllidae of Japan are named with 77 species and 7 subspecies in 20 genera, 5 subgenera and 4 subfamilies; 2 others in 2 genera are not determined specifically. One new genus, 1 new subgenus, 31 new species or subspecies and 5 new combinations are given. 21 species or subspecies are new to Japanese waters. One genus, Geminosyllis
is erected from Syllinae and one new subgenus, Regulatus
is named in Autolytus
. 46 species or subspecies, 53.4%, are currently known only from Japan, 40 others are known also from other areas.