Figure 3

Maximum-intensity projections of confocal laserscanning image stacks providing an overview of the muscle system of a single zooid of Hislopia malayensis. (a) F-actin staining. Solely the parietal muscles are associated with the cystid. Most muscles of the zooid are present at the distally situated aperture, which continues proximally into the polypide. Prominent retractor muscles run from the distal end of the zooid to the lophophoral base. From the lophophoral base the digestive tract starts with the pharynx, followed by the esophagus, which both possess mostly striated ring musculature. The adjoining proventriculus is the most prominent region of the digestive tract and possesses only smooth ring musculature. The caecum carries several distinct ring muscles and two longitudinal muscles at its proximal tip. The intestine possesses only smooth, longitudinal musculature. (b) Different zooid of H. malayensis similar as in (a) but also with cell nuclei stained with DAPI to provide a clearer picture of the cystid wall and its outlines. Also note the early bud on the right side. Abbreviations: am - apertural muscles, cae - caecum, clm - caecal longitudinal muscle, cp - communication pore, cw - cystid wall, ds - diaphragmatic sphincter, es - esophagus (cardia), int - intestine, lb - lophophore base, o - orifice, pm - parietal muscles, pv - proventriculus, rm - retractor muscles, ts - tentacle sheath, v - vestibulum, vwm - vestibular wall musculature, yb - young bud.