Haterumadienone (1), a ring-contracted derivative of puupehenone (2), was isolated from a sponge Dysidea sp., along with the artificial acetone adducts 3 and 4 of a trione hydrate 5 which could be detected in the sponge. The structures of I and the acetone adducts 3 and 4 were successfully determined by detailed spectroscopic analysis. These compounds showed the ability to inhibit the division of fertilized sea urchin eggs.