Morphological maturation level of the esophagus is associated with the number of circumesophageal muscle fibers during archenteron formation in the starfish Patiria (Asterina) pectinifera.

In echinoderms, the circumesophageal muscle is mesodermal in origin. Several studies of sea urchins have reported that the molecular events of myogenesis occur during the differentiation of the circumesophageal muscle in early embryogenesis. In contrast, few detailed reports have examined the differentiation of the circumesophageal muscle in larval starfish. Here, we examined the temporal-numeric distribution and differentiation of esophagus circular muscle fibers in the starfish Patiria pectinifera by using rhodamine-phalloidin staining. Muscle fibers were not detected in mouth-forming larvae, but a mean of about 10 muscle fibers was observed in 48-h larvae, and about 26 bundles were observed after 60 h. During the next 12 h, the number of muscle fiber bundles increased slightly to about 31 bundles and was stable until 96 h.