Direct development in Southern Australian cowries (Gastropoda : Cypraeidae)

Abstract

Direct development is described in three species of Zoila, three species of Notocypraea and one species of Austrocypraea from the temperate waters of southern Western Australia. Females lay egg-masses like those of tropical cowries but only one embryo develops in each capsule and it hatches at a crawling snail stage. Fecundity is low. Brooding lasts from 40 to 55 days. The ecological and phylogenetic significance of these observations is discussed and compared with tropical species of Cypraeidae, which have high fecundity, incubation periods of 11-18 days and planktotrophic veligers. As a provisional hypothesis, it is suggested that direct development in the southern Australian cowries evolved very early in the history of the family and that it is a successful reproductive strategy in the southern temperate zone because of the lower temperature, lower diversity, higher rates of planktonic predation and greater seasonality of planktonic food resources at these latitudes than in the tropics where planktotrophy has greater selective advantage.