ABSTRACT
Spines and venomous globiferous pedicellariae are remarkable external appendages which actively participate in the echinoid defense, particularly against predatory starfishes. Indeed, when the echinoid Sphaerechinus granulans is attacked by the asteroid Marthasterias glacialis, the spines diverge from the stimulated area while the globiferous pedicellariae inject their venom into the intruder’s tissues. In order to determine the nature of the asteroid stimulus which induces this defensive behaviour, pieces of echinoid body wall bearing quiescent appendages were stimulated by an asteroid podium, a mechanical and a neutral stimulus, and a chemical stimulus. Stimulation by asteroid podial crude extract provokes in 100% of cases the alarm reaction of globiferous pedicellariae and in 90% of cases the divergence of the spines. These results demonstrate that the behaviours of the globiferous pedicellariae and the spines provoked by the asteroid are induced by specific chemical stimulus.
