Studies in the Physiology of Commensalism. III. The Polynoid Genera Acholoë, Gattyana and Lepidasthenia

The commensal polynoid Acholoë astericola (Delle Chiaje) exhibits a powerful positive response on contact with its host, Astropecten irregularis (Pennant). This response is only relatively specific, Acholoë demonstrating it to a number of starfish that do not serve as host in Plymouth waters. All living host tissue has some attraction for the commensal; and the attractant is apparently released in quantity in the stomach of the host. Passage of time (apparently as long as tissue remains alive) and chilling do not markedly alter the attractiveness of isolated host tissue. Temperatures above 450 C. alter or abolish its attraction. The extreme instability of the attractant has so far made it impossible to demonstrate its presence in extracts. Evidence is presented that the attractant is rapidly oxidized. Experiments with the scale-worms Gattyana cirrosa (Pallas) and Lepidasthenia argus Hodgson, commensal respectively with Amphitrite johnstoni Malmgren and A. edwardsi Quatrefages, indicate that a chemotaxis to the host may be of relatively minor importance in governing the behaviour of these commensals.