Sphaeralcyon weddellensis n. gen. et n. sp. is described and illustrated from three colonies collected in the eastern Weddell Sea on the Polarsterncruises ANT V/3 and ANT VI/3. The new genus is compared with three closely related alcyoniid genera, all having capitate or mushroom-shapedcolonies and dimorphic polyps. Sphaeralcyon is readily distinguishable from Malacacanthus by the presence of sclerites (absent in this lattergenus), and from Anthomastus by sclerite shape, mainly in the form of tuberculate spheroids, and by the horny periderm on the stalk (absent inAnthomastus). Sphaeralcyon also differs from Verseveldtia in the set of sclerites, which are elongate spiny rods and a different type of tuberculatespheroid, and in the presence of eight-points as anthocodial armature (absent in Verseveldtia). The discovery of this new genus lends furthersupport to the notion that diversity in benthic communities in Antarctica is higher than suggested by previous studies.