RELATIONSHIP BETWEEN GROWTH, DIFFERENTIATION, AND LENGTH OF LARVAL LIFE FOR INDIVIDUALLY REARED LARVAE OF THE MARINE GASTROPOD,CREPIDULA FORNICATA

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Abstract
Larvae of the gastropod C. fornicata were reared individually through spontaneous metamorphosis in clean glass containers at constant temperatures ranging from 15.degree.-29.degree.C. Each larva was examined daily. Growth rates were determined from periodic measurements of individual shell length. Differentiation rates were estimated as (days to development of gill rudiments)-1 and as (days until shift from larval to adult shell geometry)-1. Growth ceased abruptly in a majority of the larvae in each treatment, over the size range 900-1100 .mu.m shell length. Larvae continued to ingest phytoplankton during this period, and growth resumed at a normal rate following spontaneous metamorphosis. An inverse correlation was observed between rates of larval growth and length of larval life through spontaneous metamorphosis. Individual growth rate prior to competence was significantly correlated with rate of individual differentiation. Rates of differentiation and growth were comparable predictors of when spontaneous metamorphosis would occur. The results are consistent with the hypothesis of a preprogrammed end to larval life in the planktotrophic larvae of C. fornicata, although the factors responsible for initiation of gill development and the shift in shell morphology are apparently not directly related to progress towards the point at which the larva spontaneously metamorphoses to the benthos.