Abstract A common Great Barrier Reef sponge, previously attributed to the genus Spongia , is described as new and placed in a new genus Rhopaloeides . This genus includes Spongiidae otherwise identical to Spongia in which the cored primary fibres form simple fascicles. The genus is also characterized by its form (massive, thick broad-based lamellae or multiple fused thick clubs). The chemistry is distinctive, characterised by possession of a rare group of C 20 diterpene furanodiols, triols and their peracetates. Considerable variation in the total yield and composition of the diterpenes for different collections of R. odorabile was confusing and led to a suggestion that more than one species was represented. Field experiments in which fragments of one individual sponge were transplanted to different conditions of illumination and depth, demonstrate that the chemical variability reflects the range of environmental conditions under which R. odorabile lives rather than any genetic differences.