Development of the Seastar, Astropecten gisselbrechti Doderlein

Abstract

The entire process of development from eggs to juveniles in the seastar Astropecten gisselbrechti was observed, with special attention to the external morphology and formation of the skeletal system . The breeding season of this seastar along the coast of Tsuyazaki (33°47' N, 130°28' E), Fukuoka Prefecture, Japan, is in June. The eggs are 353 /lm average diameter, semitranslucent, and pale brown in color. Development proceeded as follows at 25°C: Embryos develop through a wrinkled blastula stage that lasts about 5 hr (from 5 hr after insemination) by total and equal cleavage. Gastrulae bearing an expanded distal portion of the archenteron hatch from the fertilization membrane 15hr after insemination. Gastrulae develop into barrel-shaped larvae 11 days after insemination. The larva is free-swimming, and is neither bipinnaria nor brachiolaria because it lacks an open larval mouth, arms , and ciliary bands. Rudiments of the adult skeletal plates appear at this time. Metamorphosis is completed 4 days after insemination, mostly by absorption of the stalk, a larval organ, or rarely by rupture of the stalk. The newly metamorphosed juvenile is 650 /lm in diameter and bears two pairs of tube-feet on each arm . This is the third reported observation of a barrel-shaped larva in asteroids.