FEEDING PATTERNS OF FISSURELLA SPECIES ON ISLA-DE-MARGARITA, VENEZUELA - USE OF RADULAE AND FOOD PASSAGE RATES

Structural differences and functional wear of the radula in three species of the gastropod Fissurella from Isla de Margarita, Venezuela, were examined using light and electron microscopy. Wear patterns indicate between 6 and 9 transverse rows of teeth are comonly used during feeding. Mechanical wear was most noticeable on the cusps of the outer lateral tooth; this wear varied from rounding (F. nimbosa) to blunting (F. barbadensis) to squaring (F. nodosa) of the cusps. Morphological changes were additionally characterized by a significant decrease in the cusp length of marginal cusps in F. nodosa and breakage of the central tooth and inner lateral teeth in F. barbadensis. Interspecific differences in wear patterns suggest that the rhipidoglossate radula may be used differently by congeneric Fissurella.Despite considerable variation, rasping rates while feeding on the same substrate were comparable among species; however, food passage rates through the digestive system differed among species studied. Fissurella barbadensis requires 12 hours to pass its food through the digestive tract, taking almost twice as much time as F. nodosa and F. nimbosa. These data highlight differences in the feeding ecology of Fissurella species and correlate well with individual activity patterns and grazing habits. © 1990 The Malacological Society of London.