Myoanatomy of the mouth cone and introvert of Echinoderes spinifurca. (A-D) 3D reconstructions of confocal z-stacks in the head region. (E-L) confocal z-stack projections of phalloidin staining in the head region. (A, C) apical view, ventral side is down. (B, D) ventral view, anterior to the top. Cell nuclei are shown in A and B, but not shown in C and D for clarity. (E-L) Phalloidin staining in the same specimen as in A-D. Series of optical cross-sections by depth through the head as indicated by dashed lines in D; ventral side is down in all images. E-I, mouth cone region; J-L, introvert region. Numbers in K refer to the ten introvert retractors. Note: introvert scalids do not contain musculature. Abbreviations: idr, introvert distal retractors; ipr, introvert proximal retractors; ios, internal oral style; mce, mouth cone external circular muscle; mci, mouth cone internal circular muscle; oos, outer oral style; osm, outer oral style muscle; pb, pharynx bulb; pil, pharynx inner longitudinal muscle; prm, pharynx retractor muscle; psm, pharynx sheath muscle; psp, primary spinoscalids. Scale bars, 30 μm.