Muscular system of atokous
pygidium and reconstruction of pygidial coelomic cavity. A-D: Confocal micrographs showing TRITC-phalloidin labelled muscles in the posterior end of the worm. A: view from the ventral side; B: view from the dorsal side; C: virtual cross-section at the level of the border between pygidium and segment addition zone; D: an optical longitudinal section showing the position of pygidial cavity between body wall musculature and hindgut muscular lining. E-G: Orthogonal sections through the series of semithin slices of the pygidium. E: cross-section; F: virtual sagittal section; G: virtual longitudinal section. H: 3D-reconstruction of the pygidial cavity and perianal blood sinus. Dotted lines in E-G mark planes of virtual sectioning. acm – additional circular muscle; an – anus; bs – blood vessels; cav – pygidial cavity; cpm – circular pygidial muscle fibers; dv – dorsal blood vessel; gl – pygidial glands; in – intestine; lm – ventral longitudinal muscle bands; opm – oblique pygidial muscles; rpm – radial pygidial muscles; sc – segmental coeloms; vpm – ventral trapezoidal transversal muscle; vv – ventral blood vessel. Scale bar 50 μm.