Summary of the development of amphioxus non-myotome somite derivatives in embryonic (A), larval (B-E) and adult (F) stages. Note that arrows indicate a change in the relative position of tissues, but it is not known whether this is achieved by active migration and/or differential growth of somitic or surrounding tissues. See the text for a detailed description of development. Abbreviations: ECL, external cell layer; EP, ectodermal epithelium; FBM, fin box mesothelium; MS, myoseptum; MSC, myoseptal fibroblast cell MY, myotome: NT, neural tube; NO, notochord. Stage abbreviations: neur, neurula; GS, gill slit; post-met, post-metamorphic juvenile.