ABSTRACT

Gastropods are the most successful group of molluscs, having adapted to almost all aquatic and terrestrial habitats. Although the Class has a long geologic record (Upper Cambrian-Recent), and some of their radular teeth (but not the membrane) are impregnated with various metals and inorganic salts, they have not been reported fossil. This is surprising considering the abundance of modern snails along any seacoast (Hipponyx ulvae occurs intertidally on sheltered estuarine beaches in populations exceeding 10,000 individuals/m.²), and the great number of teeth in a single radula (750,000 in some cases). Because the structure of the radula is relatively constant in any one snail species, it has been utilized extensively by gastropod taxonomists working with living material. Gastropods include herbivorous microfeeders. carnivorous macrofeeders, fluid suckers, and parasitic forms with extremely specialized feeding habits. Exploitation of such a wide variety of food sources is directly linked to morphological adaptations of the radula/buccal complex, and is responsible for the bewildering complexity of gastropod radulae. As shown by recent scanning electron microscope studies, the radula is a key to the snail's feeding habits. may provide insight into their substrate preference, and allows inference of predator-prey relationships. If found fossil, radulae could furnish paleontologists with a valuable paleoecologic, and conceivably, biostratigraphic tool. This paper describes the biology, boring posture, probable boring mechanics, and ultrastructure of the radula of Thais haemastoma, the common Gulf Coast oyster "drill", and demonstrates the effect of this gastropod on its chief prey, the edible oyster, Crassostrea virginica. The first SEM analysis of its radula (modified rachiglossan--1:1:1 with exaggerated "bending plane") is presented with the suggestion that micropaleontologists initiate a careful search for snail radulae or radular fragments in subfossil (Holocene) and older sedimentary rocks.