Myogenesis during the budding process of Hislopia malayensis. Maximum-intensity projections of confocal laserscanning image stacks. (a) Early budding stage showing the polypide anlage and the first anlagen of the developing apertural and retractor muscles at its distal and proximal side, respectively. (b) More advanced budding stage with distinct tentacle anlagen (asterisk), in which the cystid of the bud has widened distally and the apertural and retractor muscle anlagen have grown and are more pronounced. (c) Advanced budding stage where first anlagen of the digestive tract musculature have formed and the parietal muscles are present laterally of the polypide anlage. Both, the apertural and the retractor muscle anlagen are most prominent. The former consists of loosely smooth muscle fibres, whereas the prospective retractor muscles have differentiated into two elongated muscle fibre bundles. (d) Almost completely developed zooid where most parts of the digestive tract, especially the most prominent proventriculus, are formed similar to the adult. Compare to Figures 3 and 4 for details on the musculature of adult specimens. Abbreviations: am - apertural muscles, ama - apertural muscle anlage, cae - caecum, ds - diaphragmatic sphincter, dt - distal tip of the cystid of the bud, dtm - developing digestive tract musculature, ep - epizooic organism, int - intestine, lb - lophophore base, pa - polypide anlage, pma - parietal muscle anlage, pm - parietal muscles, pv - proventriculus, rm - retractor muscles, rma - retractor muscle anlage, vwm - vestibular wall musculature.