Ultrastructural study of the ovary of the sessile scyphozoan, Haliclystus octoradiatus (Cnidaria: Stauromedusae)

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Abstract
An ultrastructural study of the ovary of the sessible jellyfish, Haliclystus octoradiatus, indicates that it is fundamentally different from that of other scyphozoans and is the most structurally complex within the class. Oocytes develop within a series of spherical, sac‐like ovarian follicles consisting of an enlarged intercellular space between two layers of subumbrellar gastrodermis. Developing oocytes are largely restricted to a thin germinal epithelium at the periphery of each follicle and gradually migrate toward the lumen as they mature. Individual oocytes are surrounded by early germ cells and follicle‐like accessory cells of presumed somatic origin. Similar folliclelike cells have not been described in the Cnidaria previously. Vitellogenesis appears to involve the combined activity of the Golgi complex and associated rough endoplasmic reticulum. Ovarian morphology may be helpful in deciphering phylogeneitc relationships within the Cnidaria.