The spiral-tufted bryozoan (Bugula neritina) is being studied for a potential Alzheimer's disease and cancer drug—but it's not the bryozoan that makes the chemical. The chemical, found in the bryozoan's tissues, is produced by its bacterial endosymbiont, Candidatus Endobugula sertula. In exchange for a protective home in the bryozoan's tissues, the bacteria produces a chemical called a bryostatin that makes the bryozoan larvae taste bad to predators.
Read more about drugs from the sea in this interview with Shirley Pomponi, medical sponge hunter.
Reference: Sharp KH, SK Davidson, and MG Haywood. 2007. Localization of ‘Candidatus Endobugula sertula’ and the bryostatins throughout the life cycle of the bryozoan Bugula neritina. The ISME Journal 1, 693–702.