Some aspects of the biology of the sunstar Crossaster Papposus (L.)

Abstract

Whereas Asterias has been demonstrated to use force without recourse to a toxin to open mussels (Mytilus edulis), Crossaster has an unusual feeding behaviour in which, since force appears not to be the method normally employed to open its bivalve prey, by implication some toxic substance is. Whether this is or is not a component of the normal digestive fluid is not known, and since there was no indication that any permanent shell gape of the mussel prey was being utilized, it is possible that entry may be facilitated by voluntary opening of the valves. The fact that some mussels which did not recover from the early stages of an attack by Crossaster have no evidence of peripheral digestion is thought to indicate the entry of a fluid rather than stomach tissues.

Both living individuals of Crossaster and its watery extracts cause avoidance and escape reactions by Asterias, but whereas live Crossaster and its watery extracts cause little or no response by live Buccinum undatum, extracts of Crossaster are highly toxic to the isolated radula muscle of Buccinum (Mackie, pers. comm.). However, although substances produced by living and dead Crossaster cause responses in living organisms and muscle preparations, and Crossaster flesh has a reported toxicity when ingested by cats, this must not be extrapolated to infer that Crossaster uses a toxic substance to overcome its prey. The described relationship between the toxic and repellant properties exhibited by Crossaster can only be fully understood by careful biochemical analysis.