Abstract: Gastropod Radulae: Their Potential in the Fossil Record

Paul R. Krutak

Gastropods are the most successful group of mollusks, having adapted to almost all aquatic and terrestrial habitats. Although the class has a long geologic record (Late Cambrian-Holocene), and some of their radular teeth (but not the membrane) are impregnated with various metals and inorganic salts, fossil teeth have not been reported. This is surprising in view of the abundance of modern snails along any seacoast (Hipponyx ulvae is present intertidally on sheltered estuarine beaches in populations exceeding 10,000 individuals/sq m) and the great number of teeth in a single radula (750,000 in some). 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. Ga tropods 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 linked directly to morphologic adaptations of the radula/buccal complex, and is responsible for the bewildering complexity of gastropod radulae. As shown by scanning-electron-microscope studies, the radula is a key to the snail's feeding habits, as it may provide insight into their substrate preference and allows inference of predator-prey relations. 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 haemastom , 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") suggests that micropaleontologists should initiate a careful search for snail radulae or radular fragments in subfossil (Holocene) and older sedimentary rocks.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas