ABSTRACT
Tonna galea, a very large tonnid living on mud and detritic bottoms in the Mediterranean, is a specialized predator of holothurians. It is equipped with a partially invaginable and highly extensible proboscis, which is capable of engulfing prey. We kept two specimens in the laboratory and fed them with four holothurian species, Holothuria polii, H. tubulosa, H. forskali, H. sanctori, to observe their responses to mollusk attacks. Holothurians have developed various antipredator mechanisms in response to predation. These include a tough integument, toxic and noxious skin and organs, body swelling, autotomy and evisceration. Most holothurians use one or more of these responses. All of the holothurian species involved in the feeding trials perceived the predator very late, generally when they were touched by the tentacles. The immediate responses of the prey were aimed to inhibite engulfment and allow a possible escape. To a greater or lesser degree, each of the species presents one or more reactions to attacks by Tonna, wich generally regard modifications in body size, shape and surface conformation. Generally, there was an immediate erection of the papillae and contraction of the body into a U-shape. Sometimes, holothurians attempted to break the gastropod’s hold by trying to climb onto its shell. Upward movements were the only performances which occasionally ended with a successfull escape.
