Three new chamigrenes, compound 1, acetyldeschloroelatol 2 (2-bromo-1,1,9-trimethyl-5-methylenespiro[5.5]undec-8-en-3-yl acetate), and acetylelatol 4 (2-bromo-8-chloro-1,1,9-trimethyl-5-methylenespiro[5.5]undec-8-en-3-yl acetate), and the known metabolites deschloroelatol 3, elatol 5, 8-acetylcaespitol 6, and caespitol 7 have been isolated from the sea hare Aplysia dactylomela. The structures of 1, 2, and 4 were determined on the basis of spectroscopic evidences. The in vitro cytotoxicity of six of these compounds against two cancer cell lines (HeLa and Hep-2) and nontumoral Vero cells was evaluated. The results support the hypothesis that the acetate derivatives decrease the toxicity of the corresponding alcohols in a strategy to store toxic metabolites acquired through the diet.