Responses of Five Holothurian Species to Attacks by a Predatory Gastropod, Tonna perdix

Abstract

In the laboratory Tonna perdix attacked and often engulfed individuals of five holothurian species. Two species, Stichopus chloronotus and S. horrens, sometimes escaped attacks by shedding a piece of body wall and bounding away from the predator. Bounding employed an exaggerated, direct arching peristalsis and was much faster than ordinary crawling. The general response of each of the other three species, Holothuria atra, H. cinerascens, and H. hilla, was a shortening of the body lengthwise accompanied by a swelling of the body into a spherelike shape. This response was not usually effective as an escape maneuver. Only H. hilla eviscerated during attacks and this was a direct result of penetration of the visceral cavity by the tonnid radula.