Behavioral defenses of Crepidula fornicata against attack by Urosalpinx cinerea

Two behavioral defenses of the slipper shell Crepidula fornicata (L.) against attack by the oyster drill Urosalpinx cinerea (Say) are described: (1) Jabbing: when an oyster drill approaches, the slipper shell lifts the edge of its shell, extends the head and, with the radula, pricks or rasps the foot of the predator, which instantly retracts into its shell; sometimes, after repeated approaches, the oyster drill moves away. (2) Pivoting: when an oyster drill mounts C. fornicata, the latter slowly and repeatedly rotates its shell in a horizontal plane at a constant rate and through a constant arc. If this action brings the predator's shell to bear against an obstacle, motion ceases and C. fornicata maintains the pressure until the oyster drill is dislodged. These aggressive tactics are adaptive defensive measures for a nearly sessile prey otherwise highly vulnerable to oysterdrill attack.