DEVELOPMENTAL PATTERN AND ADAPTATIONS FOR REPRODUCTION IN NUCELLA CRASSILABRUM AND OTHER MURICACEAN GASTROPODS

Abstract

Eggs of N. crassilabrum range from 204-293 .mu.m in diameter (mean 240 .mu.m). Only 6.6-7.9% are fertile; the remaining ones are ingested as nurse eggs. Embryos metamorphose before hatching. Prehatching time ranges from 55-80 days according to seasonal temperature fluctuations. Hatching size varies from 0.82-1.3 mm, depending on number of nurse eggs ingested/embryo (from 3-20). The number of fertile embryos/capsule (10-122) depends on capsule size. Hatching type and hatching size shown by N. crassilabrum agree with those of other muricaceans living in similar habitats. Prehatching time and hatching size data of various muricaceans are analyzed to determine to what extent they influence embryonic nutrition, i.e., the presence of nurse eggs or large and fertile self-sufficient eggs. Provision of nurse eggs for embryos is common among intertidal muricaceans, and this mode of nutrition seems to be favored in such habitats to reduce developmental time. Providing the yolk as nurse eggs, seems to contribute to a larger hatching size, as suggested by some subtidal muricaceans with similar embryo support patterns.