From the sea hare Stylocheilus longicauda we have isolated, in addition to the previously reported aplysiatoxins (1, 2), a novel nontoxic amide of composition C₂₈H₄₄ClNO₆. Stylocheilamide (3) is a tertiary amide constructed of a methoxyolefinic C₁₄ acid and a methyl(2-chloro-3-cyclohexyl-2-propenyl)amine. The highly functionalized carbocyclic ring gives rise to a related compound 4, differing only by the elements of HOAc. The structures have been elucidated by spectral analysis and chemical degradation. A key degradation product (8) was crystalline and its structure was determined by X-ray diffraction.