Fig. 6

Apertural muscles of selected ctenostome bryozoans. a Arachnidioidea, Nolella dilatata. Lateral view of the apertural muscles. Volume rendering. (B&C) Paludicelloidea, Paludicella articulata. Volume rendering. View of the apertural area, b Frontal side. c Basal side. d Walkerioidea, Mimosella sp., erect form. Lateral view, Maximum intensity projection. e Alcyonidioidea, Alcyonidium diaphanum. Overview of two adjacent zooids. Note the prominent orificial sphincter and the remaining diffuse apertural musculature. (F&G) Alcyonidioidea, Ascorhiza mawatarii. f Lateral view of the musculature of the aperture showing a prominent orifical sphincter and less conspicuous diffuse apertural muscles. Maximum intensity projection. g Optical section of the apertural area showing the diaphragmatic sphincter with the collar just underneath the orificial sphincter. Abbreviations: a – aperture, am – additional apertural muscle, c – collar, da – diffuse apertural muscle, ds – diaphragmatic sphincter, l - lophophore, os – orificial sphincter, pb – parieto-vaginal bands, pd – parieto-diaphragmatic muscle, ph – pharynx, pm – parietal muscle, pv – parieto-vestibular muscle, rm –retractor muscle, ts – tentacle sheath, vw – vestibular wall muscle