Drilling predation on recent clypeasteroid echinoids from the Red Sea

In contrast to mollusks, drilling predation on echinoids rarely has been in vestigated. Two minute clypeasteroid echinoids (Fibularia ovulum and Echino cyamus crispus) from the Northern Bay of Safaga, Red Sea, Egypt, were exami ned for drill holes using numerous samples collected from several bottom fa cies. Out of 1076 tests, 566 (52.6%) were drilled (45.8%-Fibularia ovulum, 70.7%-Echinocyamus crispus). The cylindrical shape of drill holes, their sm all size (mean diameter=0.9 mm) acid-etching traces, and current biological knowledge suggest that these holes were produced by cassid gastropods. All holes are complete and unrepaired and tests with multiple holes are rare ( 6%) suggesting a very high success rate of predatory attacks. The other ech inoids in the study area are rarely or never drilled. The minute clypeaster oids are preferred prey due, most likely, to their abundance and poor defen sive mechanisms. Predation frequencies vary greatly, both within and across bottom facies, reaching up to 83%. Such variation may hamper reconstructio ns of the long-term patterns in the fossil record of drilling predation on echinoids. Drillhole outlines are highly variable due, most likely, to the presence of plate boundaries and pores in the prey tests. This suggests tha t such variation should not be used as sole evidence for presence of multip le predators or for variable predatory behavior. Predators drill preferenti ally the aboral (dorsal) side of the test (84.9%-F. ovulum, 99% -E. crispus ), but do not appear size-selective. The drilling frequencies appear to be independent of the taphonomic state of the tests, suggesting that the prefe rential destruction of drilled tests during the pre-burial (biostratinomic) taphonomic phase is unlikely. The drilling frequencies in minute clypeaste roids are comparable with the highest frequencies previously reported for o ther modern echinoids, and are much higher than those typically reported fo r fossil echinoids as well as for other Recent and fossil prey of drilling predators.