The Toheroa, Amphidesma ventricosum Gray (Eulamellibranchiata), Development and Growth

Abstract

A short historical account of the toheroa of New Zealand is given, and its beach habitat is described. Development of the reproductive organs, spawning, and early development are described up to the stage when the free-swimming form settles on the beach. Types of sand and the particular character of the zone in which toheroa are found are described. Length frequency data and shell zones are used to demonstrate differences in growth rate on the four principal beaches. Length frequency data are shown to give a much higher rate than shell zones indicate, probably because of the long spawning season. Growth of different parts by weight is studied. Of several hundred toheroa marked with a file, two were recovered after 6 weeks, giving a growth rate in agreement with that estimated. One small specimen kept in an aquarium for 8 weeks made no growth. The existence of off-shore stocks is briefly discussed.