Nine sesterterpenes 1-9 have been isolated from a Dictyoceratid sponge, Strepsichordaia lendenfeldi, collected on the Great Barrier Reef, Australia. Seven of these compounds are new, one [4] had been reported previously as a semisynthetic product, and one [5] had been isolated previously from Carteriospongia foliascens. Unambiguous 13C- and 1H-nmr assignments have been made for 1 based on extensive 1D and 2D high field nmr experiments, which enabled 13C-nmr assignments to be made for 2-9. Significant growth inhibitory effects with tested cancer cell lines are reported for compounds 1-8.