turritellid, (genus Turritella), any of several species of gastropods (snails) abundantly represented in fossil and living form from the Cretaceous Period, which began about 144 million years ago, up to the present. Many forms or species of turritellids are known; all are characterized by a high, pointed shell that narrows greatly at the apex. The shell is frequently ornamented by lines, ridges, or grooves.