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Structural changes of gonads during artificially induced gametogenesis and spawning in the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae)

Published online by Cambridge University Press:  01 September 2010

Hideki Ikeda*
Affiliation:
Graduate School of Biosphere Science, Hiroshima University, 4-4 Kagamiyama 1-Chome, Higashi-Hiroshima 739-8528, Japan
Kohzoh Ohtsu
Affiliation:
Oki Marine Biological Station, Faculty of Life and Environmental Science, Shimane University, 194 Kamo, Okinoshima-cho, Oki-gun, Shimane 685-0024, Japan
Shin-Ichi Uye
Affiliation:
Graduate School of Biosphere Science, Hiroshima University, 4-4 Kagamiyama 1-Chome, Higashi-Hiroshima 739-8528, Japan
*
Correspondence should be addressed to: H. Ikeda, Graduate School of Biosphere Science, Hiroshima University, 4-4 Kagamiyama 1-Chome, Higashi-Hiroshima 739-8528, Japan email: [email protected]

Abstract

We conducted a histological investigation of the ovaries and testes during the gametogenesis and spawning in the giant jellyfish Nemopilema nomurai, which has bloomed in East Asian marginal seas almost annually since 2002. Oocytes arising from the ovarian epithelium make intimate contact with special epithelial cells, called trophocytes, which have microvilli on the subgenital sinus side, Golgi complexes and vesicles in the cytoplasm. In the early vitellogenic stage, yolk bodies occur in the ooplasm adjacent to the trophocytes, suggesting that the trophocytes transfer nutrients from the subgenital sinus to the oocyte. Later, yolk bodies are formed by the Golgi complexes in the entire ooplasm and accumulate until the oocyte matures. In the late vitellogenic stage, the oocyte separates from the trophocytes and forms microvilli on its surface, indicating nutrient uptake from the surrounding mesoglea. Nutrient support from the trophocytes in the early vitellogenic stage may make the oocytes mature rapidly after medusae are physically damaged. Microvilli-rich epithelial cells also associate with sperm follicles where spermatocytes arise from the follicle cells and accumulate, but their function in nutrient uptake is possibly less than that of trophocytes according to their morphology. During ovulation, which takes 1.5 hours after light exposure, trophocytes separate from each other and make an ovulation pit where the oocyte passes out to the subgenital sinus with the surrounding basal lamina. Spermiation occurs 5–20 minutes after light exposure, and spermatozoa are liberated through the spermiation pit that was formed by which the microvilli-rich cells dissociate. The trophocytes in ovaries and microvilli-rich cells in testes have important roles not only in the gametogenesis but also in the spawning of N. nomurai.

Type
Research Article
Copyright
Copyright © Marine Biological Association of the United Kingdom 2010

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