Naticid Gastropods May Kill Solenid Bivalves without Boring: Ichnologic and Taphonomic Consequences

Abstract

A somewhat novel but nonetheless important predator-prey relationship was described by Turner (1955) and Schneider (1982): the naticid gastropod Polinices duplicatus commonly captures the solenid bivalve Ensis directus by attacking its foot rather than by drilling through its shell. From a paleoecologic or taphonomic standpoint, the most significant result is numerous dead in-situ individuals of E. directus, the valves of which remain pristine. In other instances the valves are retained partly within the burrow but project above the substrate surface, reflecting a futile attempt by the clams to escape. Frequently clams burrow widely through the sediment in various attempts at flight, some successful and others not. Such behavior evidently is widespread among morphologically and ecologically equivalent mollusk species (e.g., Colbath, 1985, p. 858), and was observed recently on tidal flats near Inchon, Korea. These tidal flats, which are generally similar to ones described by Lee et al. (1985), are replete with epibenthic and endobenthic mollusks. Among them is the razor clam Solen strictus, ecologically equivalent to Ensis directus, and the gastropod Euspira fortunei, which is equivalent to Polinices duplicatus. Populations of S. strictus FIGURE I-Burrows and in-situ live individuals of the solenid bivalve Solen strictus in muddy sediments of a macrotidal flat near Inchon, Korea. These well-maintained domiciles are lined with a smooth, thick layer of mucus-impregnated sediment; basal enlargements represent dilations of the foot. Escape burrows are considerably more irregular and ephemeral; yet, all burrows are arcuate, as governed by the longitudinal curvature of the animal itself.