STUDIES IN THE PHYSIOLOGY OF COMMENSALISM

1. THE POLYNOID GENUS ARCTONOË

¹ University of California, Santa Barbara College

1. Apparatus was developed which made it possible to determine whether commensals of the polynoid genus Arctonoë are attracted by specific substances to their hosts and whether they can distinguish between water coming from an aquarium containing their host and sea-water alone or water from non-host.

2. Arctonoë fragilis (Baird) commensal with the star Evasterias troschelii Stimpson are clearly attracted to their host and can distinguish between water coming from their host and sea-water alone. Arctonoë (pulchra-vittata?) commensal with the cucumber Stichopus are likewise attracted to their host.

3. Arctonoë fragilis commensal with Evasterias are not attracted to the non-host star, Pisaster, occurring in the same immediate environment as their host. Arctonoë (pulchra-vittata?) commensal with the cucumber Stichopus are likewise not attracted to the non-host Cucumaria.

4. Arctonoë (pulchra-fragilis?) commensal with the mud-star Luidia are not attracted, under these experimental conditions at least, to their own host. Arctonoë fragilis commensal with Evasterias are not attracted to the mud-star Luidia, in spite of the fact that Luidia may be a host of fragilis. These results are perhaps inconclusive, because injury substances may have been released into the apparatus by the mud-stars.

5. Cross experiments (A. fragilis from Evasterias tested against Stichopus and A. pulchra-vittata from Stichopus tested against Evasterias) indicate that attractants released by the two hosts are not the same, since neither commensal is attracted to its relative's host.