Six new (1-6) spongian-16-one analogues have been characterized from the Australian nudibranch species Goniobranchus collingwoodi, along with four known spongian-16-one derivatives. The structures and relative configuration were suggested by spectroscopic analyses informed by molecular modeling. Dissection of animal tissue revealed that the mantle and viscera differ in their terpene composition. Whole body extracts were not toxic to brine shrimp (Artemia sp.), but were unpalatable to palaemon shrimp (Palaemon serenus) at a concentration found within the nudibranch. Individual terpenes were not cytotoxic to human lung (NCIH-460), colorectal (SW620), and liver (HepG2) cancer cells.