The new iso-, nor-, and dinor-spiculoic acids A (1, 2, and 3, respectively) with a rare spiculane skeleton were isolated from the marine sponge Plakortis zyggompha, collected in the waters south of Martinique. The structural determination of the compounds was based on 1D and 2D NMR studies and mass spectral determinations. Compounds 1 and 2 showed weak cytotoxicity against the two tumor cell lines A549 and HT29.