Fig. 1

Schematic overview of one everted phylactolaemate zooid with the main structures and musculature shown. a: The polypide is surrounded by the protective cystid wall. The lophophore carries all tentacles. The u-shaped digestive tract is divided into pharynx, esophagus, cardia, caecum and intestine, which terminates with the anus in the tentacle sheath outside the lophophore. The paired retractor muscles originate from the proximal body wall and insert at several locations of the polypide. When the animal is retracted the tentacle crown is surrounded by the tentacle sheath. The connection between the outer cystid and the tentacle sheath is formed by the vestibular wall. b: Schematic overview of the main parts of the muscular system in Pectinatella magnifica. The tentacles contain two longitudinal muscle bands, a frontal (dark blue) and a abfrontal (blue) one. The epistome also possesses distinct musculature (brown). In Pectinatella they traverse the coelomic cavity. The lophophoral arms contain longitudinal muscle fibers (orange). In the ring canal muscular elements (purple) are at the base and on the distal side. The digestive tract contains exclusively ring musculature (grey) and the funiculus (green) is supplied by fine longitudinal muscles (black). The body wall contains two or three layers of musculature in Pectinatella (black dashed lines). The tentacle sheath contains a fine mesh of longitudinal and circular musculature (cyan). Abbreviations: a - anus, ar – aperture region, bw – body wall, ca - cardia, cae - caecum, cw - cystid wall, db - duplicature bands, dg - digestive tract, e - epistome, es - esophagus, f - funiculus, cg - cerebral ganglion, int - intestine, la – lophophoral arm, o - orifice, ph - pharynx, rc – ring canal, rm. - retractor muscle, t – tentacles, ts - tentacle sheath, vd – vestibular dilatators, vw - vestibular wall