A new hexacyclic pyridoacridine alkaloid, nordehydrocyclodercitin (1), from an ascidian, Aplidium sp., cf. Aphdium cratiferum collected at Arab Reef, Great Barrier Reef, Australia is reported. Nordehydrocyclodercitin is structurally related to stellettamine (2) and cyclodercitin (3), which are sponge metabolites, and cycloshermilamine D (4) which was isolated from the marine tunicate Cystodytes violatinctus. The structure of nordehydrocycloderci tin was determined by interpretation of spectroscopic data, particularly those obtained from HMBC correlations, and by comparison with reported data for known related pyridoacridine alkaloids.