DEVELOPMENT OF A TRUE OVOVIVIPAROUS SEA STAR, ASTERINA-PSEUDOEXIGUA-PACIFICA HAYASHI

Asterina pseudoexigua pacifica is a true ovoviviparous asteroid in that its development and metamorphosis occur within the spatial hermaphroditic gonad. From the middle of June to the middle of July, the gonad contains numerous embryos and juveniles in various stages through metamorphosis. The opaque, greenish yellow mature ovum is 450 mu-m in diameter. Development is direct. Embryos develop through wrinkled blastula and gastrula stages into a pear-shaped brachiolaria with three arms. The general process is similar to that of asteroids having direct development. Newly metamorphosed juveniles are released from the gonopores. Peak release occurs in the middle of July. The maximum number of juveniles released from an adult is about 1300. The juvenile is 900 mu-m in diameter and has two pairs of tube-feet in each arm; the skeletal plates are well developed. The present results are compared with those of other true viviparous echinoderms.