AbstractA new species of Perkinsiana, P. riwo, is described from near Madang on the northern coast of Papua New Guinea. This species is smaller than most species of Perkinsiana and is distinctive in having extremely short handles on the thoracic and abdominal uncini. Perkinsiana riwo is similar to P. antarctica (Kinberg) in that they both brood batches of larvae attached to one or more ventral radioles of the radiolar crown. Perkinsiana riwo is a simultaneous hermaphrodite with oocytes in anterior abdominal chaetigers and sperm and spermatids in the following abdominal chaetigers. Sperm have a nearly spherical head with a cap-like acrosome and 4–5 spherical mitochondria surrounding the base of the free flagellum. Oocytes reach a maximum size of around 200 µm in diameter. Larvae develop inside individual egg capsules in the cocoon until they have three thoracic chaetigers. They then escape from the capsules and cocoon and swim for up to two days before settling.