HETEROSTOPHIC SHELLS AND PELAGIC DEVOLOPMENT IN TROCHOIDEANS: IMPLICATIONS FOR CLASSIFICATION, PHYLOGENY AND PALAEOECOLOGY

Publisher Website
Google Scholar
Abstract
Four species of archeogastropods, presumed members of three subfamilies of the trochidae, exhibit significant differences in developmental modes and shell coiling. All four species have lecithotrophic development which is reflected in their inflated pausispiral protoconchis; however, Margarites marginatus and Lirularia succincta have benthic development in gelatinous masses, while Margarites pupillus and Calliostoma ligatum have pelagic embryos and swimming larvae with a potential for dispersal over a period of a week or longer. These modes cannot be deduced from the size of the egg, the size or shape of the protoconch, or the size or relative prominence of female pallial reproductive structures. The protoconch of C. ligatum is orthostrophically coiled, but the protoconchs of the other three species are hyperstrophically coiled although their teleconchs are orthostrophic. These three trochoidean species thus share with architectonicoideans, pyramidelloideans, opisthobranchs, and pulmonates the distinctive shell character of heterostrophy, previously unreported for archaeogastropods.