Acanthenes A(1) and B(2), two new eudesmane sesquiterpenoids, have been isolated from the marine sponge Acanthella. Acanthene C(3), the formamide analog of 1 and 2, has been isolated from the nudibranch Cadlina luteomarginata which feeds on Acanthella. The structures of 1 to 3 were solved by analysis of spectroscopic data. Acanthene A (1) appears to represent the first example of the co-occurrence a chloro sesquiterpenoid analog of sponge isothiocyanate, formamide or isonitrile sesquiterpenoids.