Benthic cnidarians are colonial marine animals that host a rich population of associated and symbiotic microorganisms. In a recent paper we described for the first time the isolation of amphidinolide P (1) from the Brazilian octocoral Stragulum bicolor. Amphidinolides and similar compounds had been previously reported only from dinoflagellates of the genus Amphidinium; thus the presence of 1 in the invertebrate opens intriguing questions on the role and occurrence of these molecules in marine ecosystems. Here we report the identification of four further amphidinolides from the same soft coral, including the known amphidinolide T1 (2) and the new analogues here named amphidinolides C4 (3), B8 (4), and B9 (5). The chemical structures have been elucidated mainly by extensive study of spectroscopic data. Cytotoxic activities of 3 and 4 were evaluated against the colon adenocarcinoma cell line HCT-116.