Its a Snail's Life
At first, the reproductive cycle of Thyca crystallina seems typical of a marine gastropod, with separate sexes and external fertilization. After mating, the female lays eggs, which develop into free-swimming larvae. The larvae go through a planktonic phase, drifting in the ocean for a time. This snail, however, has a life cycle divergence from a typical marine snail; after drifting for a time, it settles on an echinoderm host, the Blue Seastar Linckia laevigata , where it plays the role of a parasite. Evidence of this parasitic relationship goes back to the Late Cretaceous, when dinosaurs, particularly Tyrannosaurus rex , ruled the planet. The Late Cretaceous ended with the K-T extinction event; none of the dinosaurs would survive this. The planktonic larvae of T. crystallina allow dispersal, and these snails range across the Indian and Pacific Oceans. Reducing its spread is the snail’s tie to the seastar. It appears to be restricted to populations o...