Figure 4

Organization of muscular system in advanced and competent larvae of Phoronopsis harmeri. In all photographs, the apical pole of the larva is to the top. A. Photograph of live larva, lateral view, the ventral side is to the right. B – E. 3D-reconstructions of the muscular system of larvae stained with phalloidin. F – H. Z-projections of the muscular system of larvae stained with phalloidin. A. Competent larva. B. Overview of the musculature of a competent larva; lateral view. C. Musculature of anterior part of an advanced larva, lateral view. D. Collar region of an advanced larva with tentacular coelom (c2), collar ring muscle (cr), tentacle elevators (te), and tentacle depressors (td); lateral view, the ventral side is to the right. E. Apical body part of an advanced larva with apical plate (ap), paired hood depressors (hd), and esophageal musculature (es); dorsal view. F. Tentacular musculature of a competent larva. G. Overview of the musculature of a competent larva; lateral view, the ventral side is to the right. All main muscles are shown. H. Overview of the musculature of an advanced larva; lateral view, the ventral side is to the right. Abbreviations: bm – blood mass; es – esophageal musculature; eso – esophagus, lfc – laterofrontal cells of postoral ciliated band; ms – metasomal sack; st – stomach; t – tentacle; tt – telotroch.