Predation in time and space: peeling and drilling in terebrid gastropods

Abstract

Two types of predation (shell breakage at the lip by calappid crabs and drilling by gastropods) were studied in more than 6000 Recent and 1500 fossil terebrid gastropods. The occurrence of lip-peeling was assessed by the frequency of shell repair, defined as the number of repaired injuries divided by the total number of shells in a sample. This frequency is interpreted as a measure of the demonstrated importance of the shell as a protective device against peeling. In the Recent fauna, frequencies of repair are highest in the tropical Indo-West-Pacific, intermediate in tropical America, and lowest in warm-temperate areas. When comparisons are restricted to particular size classes, these geographical differences become blurred, especially among smaller shells. Slender, many-whorled species have significantly lower frequencies of repair than do terebrids with more compact shells. Samples of Terebra affinis from atolls have fewer repairs than do those from high islands or continental shores. Among fossils, there is no difference in repair between Paleogene and Neogene samples. In the Miocene, warm-temperate terebrids had frequencies of repair similar to those of tropical species. The frequency of repair is loosely correlated with the number of species of shell-peeling calappid crabs. Frequencies of drilling have been at high modern levels since Eocene time. Incomplete drill-holes are common in large Recent species, and suggest that the terebrid shell is well adapted to withstand attacks by naticid gastropods. The results of this study are consistent with those of architectural analyses of soft-bottom gastropod assemblages and with other studies on predation of gastropods.