An ultrastructural study of strobilation in Chrysaora quinquecirrha with special reference to neurosecretion

Scyphistomae and strobilae of the scyphozoan Chrysaora quinquecirrha were fixed and sectioned for electron microscopy. The polyps were divided into four classes on the basis of their stage of development: non‐strobilating (scyphistomae), neck‐formation, segmentation, and metamorphosis. Ultrastructural preparations revealed neurosecretory cells containing numerous membrane‐bounded granules in scyphistomae and necked polyps. At the time of neck‐formation the neurosecretory granules were mpst concentrated in the cell body and at segmentation, most concentrated in the axons of the neurites. By metamorphosis most of the neurosecretory product had disappeared from the axons. Other changes which appear to accompany strobilation included both a decrease in glycogen and contraction of muscles along the inner edge of the epidermis.