Life cycle of Bougainvillia bitentaculata (Hydrozoa : Anthomedusae) in Japan

Abstract

The life cycle of Bougainvillia bitentaculata in Japan is described. The morphology and the cnidome of the hydroid and the 1-day-old immature medusa are described together with egg size, spawning time, and seasonal occurrence of medusa for the first time. A marked morphological change appeared in the laboratory-reared medusae of both sexes, especially in the number of tentacles, i.e. up to eight marginal tentacles are produced in a tentacular bulb and one of the four oral tentacles branched up to five times. As described previously, usually two marginal tentacles are present in a tentacular bulb of the medusa collected in the sea, but sometimes three and rarely four tentacles were also observed during the present study.