AbstractThe title sponge is shown to contain eight new sesquiterpenoids for which a common, unusual biogenetic origin is postulated. The compounds are shown to be: (–)‐(1R*,4R*)‐3‐(3′‐furyl)methyl‐2‐p‐menthen‐7‐yl acetate ((–)‐8b); two diols separated as the monoacetates (–)‐(1S*,4R*)‐3‐(3′‐furyl)methyl‐l‐hydroxy‐2‐p‐menthen‐7‐yl acetate ((–)‐13a) and the (–)‐(1R*,4R*)‐epimer (–)‐13b, the two C(4)‐epimeric 4‐ethoxy‐3‐(1′(7′),2′‐p‐menthadien‐3′‐yl)methyl‐2‐buten‐4‐olides ((+)‐14aand (–)‐14b), (–)‐3‐(3′‐furyl)methyl‐7‐nor‐2‐p‐menthen‐l‐one ((–)‐11), (