Daily cycling of the crystalline style in the omnivorous,Deposit-feeding estuarine snail Ilyanassa obsoleta

Crystalline styles are present in nearly all bivalve mollusks, and are known to undergo cyclic changes in size and/or occurrence in many species. A few gastropod species are known to possess styles, but such cycles as may exist are unknown or not well documented. Results reported here show that Ilyanassa obsoleta (Say) in a sandflat population lose and regain their crystalline styles each day. Styles were consistently low in frequency just after dawn. The presence of this kind of rhythm in a deposit-feeding gastropod has not previously been noted. It is suggested that this cycle may have played a key role in the evolution of this widespread and numerically abundant species.