The structure of an unusual thiazole containing compound, mycothiazole (l), was established after extensive NMR analysis. It was further confirmed by exhaustive interpretation of a HREIMS spectrum. Mycothiazole was isolated from Spongia mycofjiensis collected from Vanuatu and it exhibited anthelminthic activity (in vitro) while high toxicity was observed in mice. Even though the disubstituted thiazole ring system that is present in 1 has not been previously observed in natural products chemistry, comparisons of its carbon skeleton to that of latrunculin B suggest a possible route for its biogenesis.