Abstract

Walls of egg capsules of the gastropod Crepidula fecunda Gallardo, 1979 were examined at different developmental stages during the period of intracapsular development of embryos. The weight, biochemical composition, and structural features (using scanning and transmission electron microscopy) of the capsule walls were examined at several intervals during development of the embryos to the hatching stage. Biochemical analyses were also carried out on the intracapsular fluid to identify the possible transfer of organic material from the capsule wall to the intracapsular fluid. The capsule wall is composed principally of organic matter, primarily protein (91%), plus minor lipid and carbohydrate components. The capsule wall consists of a thin, fibrous external layer, which overlies a thicker, spongy inner layer. The spongy layer has almost disappeared by the end of the developmental period, losing about 90% of its thickness. The 40% loss in weight of the capsule walls over the developmental period is due to loss of organic matter as protein. This suggests that the inner layer of the capsules dissolves and/or disintegrates as larval development advances. The levels of dissolved and/or particulate proteins in the intracapsular fluid are much higher than those typical of the seawater surrounding the capsules. This suggests that, as embryonic development proceeds, the inner capsule walls could potentially provide extra nutrients to the embryos.