Two new tambjamine class alkaloids, possessing ichthyodeterrent properties, have been isolated from the organic extracts of the marine ascidian Atapozoa sp. and its nudibranch predators. The structure of the new metabolites were elucidated through interpretation of their physical and spectral data and by comparison with spectral data for related compounds. Microscopic examination of Atapozoa considering the yellow color of the tambjamines suggested that Atapozoa is capable of the de novo biosynthesis of these metabolites. © 1991 Birkhäuser Verlag.