<jats:p>An Australian marine tunicate Aplidium sp. collected from the Great Australian Bight has been found to contain seven macrocyclic alkaloids, identified as the novel marine metabolites aplidites A-G (1)-(7). Each aplidite incorporates a hitherto undescribed orthonitrite functionality. Structures for the aplidites were secured by detailed spectroscopic analysis, derivatization and degradation.