From the deep violet, encrusting marine sponge Chelonaplysilla violacea, two rearranged spon- gian diterpenes, aplyviolene, (1R′, l′S*, 3′aR*, 5R*, 6R’, 8R*, 8′aS*)-3-oxo-8-(1′, 4′, 4′-trimethyl-8′- methylenedecahydroazulen-1′-yl)-2, 7-dioxabicyclo[3.2.1]oct-6-yl acetate (1), the acetoxy derivative, aplyviolacene (2), (5R*, 8S*, 9S*, 10R*, 13S*, 14R*, 15S*, 16R*)-spongian-15, 16-diyl diacetate (3) and (5R*, 8S*, 9S*, 10R*, 13S*, 14R*)-spongian-16-one (4) were isolated. The structures were determined by spectroscopic methods, and the structure of aplyviolene was confirmed by a single-crystal X-ray determination. The crystal structure was refined to a residual of 0·036 for 1125 independent observed reflections. The crystals were orthorhombic, space group P212121 with a 8·098(1), b 11·628(1), c 21·774(3) Å. © 1990 ASEG.