Chemical investigation of the nudibranch Glossodoris rufomarginata and its sponge prey provided additional evidence of the trophic relationship between Glossodoris nudibranchs and scalarane-containing sponges. Scalaradial (1) and its deacetyl derivative 2 were found to be the main components of the extract of the sponge, whereas a series of related scalaranes (3-7), probably derived from dietary scalaradial, were isolated from the mollusk. Two new scalarane sesterterpenes (5 and 6), exhibiting a keto functionalization at C-12, were characterized by spectroscopic methods and chemical correlations.