REPRODUCTION AND DEVELOPMENT OF THE HERMAPHRODITIC SEA-STAR,ASTERINA MINORHAYASHI

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Abstract
The breeding season of A. minor occurs during May in Kushimoto, Japan, and involves a characteristic breeding assemblage with eggs laid on the substratum in a mass spawning. The eggs are not protected by the adults. A. minor is a spatial hermaphrodite with ovaries and testes maturing simultaneously. Isolated individuals are capable of self-fertilization and such eggs develop normally. The spawned eggs are spherical, yellow and 437 .mu.m in average diameter. They attach to the substratum with a sticky jelly layer. Cleavage is total and radial. Eggs through the wrinkled blastula stage develop into a pear-shaped brachiolaria bearing 3 brachiolar arms within the fertilization membrane. About 4 days after spawning, the brachiolariae hatch from the fertilization membrane and creep on the substratum with well-developed brachiolar arms. There is no evidence of a pelagic life in the present species. One day after hatching, brachiolariae attach firmly to the substratum with the brachiolar arm and undergo a rapid transformation of the body (metamorphic climax). Metamorphosis is completed with the opening of the mouth about 10 days after spawning. The newly metamorphosed juvenile is about 700 .mu.m in diameter and each arm bears 2 pairs of the tube-feet and 1 red eye-spot at the base of the terminal tentacle. The reproduction and larval development in A. minor are unique, and the study may prove a good guideline for understanding the evolution of reproduction and development in Asteroidea.

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