Polychaetes of 31 species of Polynoidae and two species of Acoetidae from Sagami Bay and Sagami Sea are recorded from the collection made by the Emperor Showa, deposited at the Showa Memorial Insritute. Three new genera of Polynoidae,
Showascatisetosus,
Medioantenna and
Showapolynoe are described. Seven species of Polynoidae,
Showascalisetosus shimizui,
Medioantenna clavata,
Harmothoe cylindrica,
Harmothoe glomerosa,
Eunoe spinosa,
Hololepida japonica and
Lepidonotus glaber are new to science. Four species of Polynoidae,
Harmothoe spinifera,
Harmothoe praeclara,
Heteralentia ptycholepis and
Lepidonotus albopustulatus, and
Euarche tubifex of Acoetidae are recorded from Japanese waters for the first time. All species are described.