THE RELATIONSHIP OF TEMPERATURE TO THE LARVAL DEVELOPMENT OF NASSARIUS OBSOLETUS (GASTROPODA)

1. Development of the embryos of Nassarius obsoletus within egg capsules is regulated by sea-water temperature. An increase in the time required between spawning and the emergence of veliger larvae is slight between 28° and 20° C., about 0.25 day for each degree decrease in temperature. Between 20° and 16.5° C., the corresponding increase was 2 days per degree decrease in temperature. At 11.5° C., development was not completed and larvae did not emerge from their egg capsules after nine weeks. However, a large proportion of these embryos survived and developed normally through metamorphosis when placed at room temperature. 2. The growth rate of planktonic veliger larvae of N. obsoletus was greatest at approximately 25° C. The lowest temperature at which the development to metamorphosis was completed was at 16° to 17° C. There was a 46% inhibition in the growth rate of larvae between the optimum temperature and the minimum temperature at which development is completed. 3. The larval life of N. obsoletus veligers may be divided into two stages. The first of these, the "developmental period," is one during which rapid growth and morphological development occur. This is followed by the "delay period" characterized by a gradual decrease in growth rate. Reduced temperature may influence the rate of growth and consequently the length of the "developmental period." The termination of the "developmental period" comes with the "creeping-swimming stage." The duration of the "delay period" may be quite variable and is determined by the availability of a favorable sediment for settlement.