LARVAL DEVELOPMENT IN THE ASTEROID ECHINASTER ECHINOPHORUS.

1. Echinaster echinophorus off the west coast of Florida was observed to spawn, from early April to late July, two different egg types: one type is pelagic, brown to black in color and 1.0-1.3 mm in diameter, while the second is bright orange, ranges from 0.84 to 0.88 mm in diameter and settles immediately to the substratum after spawning. 2. The present study reports on external morphogenesis of Echinaster eggs of the second type. 3. Cleavage stages occurred rapidly at the laboratory temperature of 25° C with the gastrula being reached 24 hours after fertilization. By 48 hours a modified brachiolaria develops with 4 larval arms and a central sucker. Folding of the preoral lobe toward the oral surface at 7 days of growth is reported for the first time in Echinaster. 4. A chronology of larval and juvenile development is presented. 5. Larval growth rates expressed as lengths (mm) as well as juvenile growth rates expressed as ray lengths (mm) and wet weights (mg) are presented.