New records of the green-algal genus Rhipiliopsis (Udoteaceae, Caulerpales) from Papua New Guinea and the Seychelles Islands, including the description of Rhipiliopsis papuensis Coppejans, De Clerck et Leliaert, sp nov.

A new monostromatic species of Rhipiliopsis, a papuensis, is described from shaded subtidal habitats on the south coast of Papua New Guinea. Closely r elated to R. novae-caledoniae Farghaly et Denizot, it differs in having a b asally corticated stipe, a lack of wall thickenings above the dichotomies o f the blade siphons, and by its very regularly sinuous siphons that are lin ked laterally by evenly spaced cohesion papillae. New distribution records are made of R. gracilis Kraft, from the same locality as R. papuensis, and of R. echinocaulos (Cribb) Farghaly and R. madagascariensis Farghaly et Den izot from the Seychelles Islands in the western Indian Ocean. A key to the monostromatic species of Rhipiliopsis is presented.