Fig. 5

Schematic drawings of the myognesis in Siboglinum fiordicum larvae. A–C Early metatrochophore, the first septum divides body into two tagmata: common anterior segment (fr + tr) and common opisthosomal segment (o), D–F Late metatrochophore, division of the opisthosoma into segments, G–I competent larva, division of the common anterior segment into forepart (fr) and trunk (tr) and new posterior segments appear at the end of the opisthosoma. Longitudinal muscles are shown in blue, circular muscles are in red, cilia—in green, chaetae—in orange. L, V, D serve for lateral, ventral and dorsal body orientations. ca—annular chaetae, co—opisthosomal chaetae, fr—forepart segment, m—mesotroch, mc—circular musculature, md—dorsal longitudinal muscle strand, mls—longitudinal muscle of the first septum, mlvl—lateral component of the ventrolateral longitudinal muscle strand, moc1-7—the first-seventh circular muscles in the opisthosoma, mv— ventral longitudinal muscle strand, mvvl—ventral component of the ventrolateral longitudinal muscle strand, na—anterior neurotroch, np—posterior neurotroch, o—common segment of the opisthosoma, o1-o7—the first-sixth segments of the opisthosoma, p—prototroch, pe—peristomium, pr—prostomium, py—pygidium, tb—tentacular anlage, tm—circular muscles of the tb, tr—trunk segment