Molecular phylogeny and evolution of symbiosis in a clade of Indopacific nudibranchs

► Phyllodesmium is a monophyletic group. ► Symbiotic species and non-symbiotic species evolved separately. ► Xeniid-associated species represent a trophically-driven adaptive radiation. ► There may have been a reversal from a symbiotic to a non-symbiotic state.