A detailed analysis of the chemical constituents of a Caribbean specimen of Agelas sp. was carried out. Four brominated compounds (1-4) were isolated and one of them was identified as a new bromopyrrole metabolite, monobromoisophakellin (1). The structure of 1 was established from spectral studies. All compounds were tested for their antifeedant activity against the Caribbean reef fish Thalassoma bifasciatum in an aquarium assay.