Anthoarcuata graceae

Another example of a nudibranch, which probably modifies dietary metabolites to obtain more effective allomones, is seen in Aldisa cooperi (= A. sanguinea cooperi) [155]. It elaborates two fish antifeedant bile acids (104,105) that are absent in its prey, the sponge Anthoarcuata graceae, where the main steroid is 4-cholesten-3-one (106). Biosynthetic experiments starting from both labelled mevalonic acid and labelled 4-eholesten-3-one would definitely clarify, whether, the two allomones (104-105) are biosynthetized de novo by the mollusc, or if they are derived from a food source. 

Tischler, M., Ayer, S.W., Andersen, R.J., Mitchell, J.F., and Clardy, J. (1988) Anthosterones A and B, ring-contracted steroids from the sponge Anthoarcuata gracea. Can.J. Chem., 66,1173-1178. 

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