Vol. 100, No. 2 April, 1951 THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY STUDIES IN THE PHYSIOLOGY OF COMMENSALISM. 2. THE POLYNOID GENERA ARCTONOE AND HALOSYDNA DEMOREST DAVENPORT AND JOHN F. HICKOK University of California, Santa Barbara College, and David Starr Jordan Junior Hif/li School, Burbank, California In earlier experiments (Davenport. 1950), it was demonstrated that the specifi-city of the commensal polynoid worms Arctonoc fragilis (Baird) and A. pnlchra (Johnson), respectively inhabiting the starfish Evasterias troschelii Stimpson and the sea-cucumber Sticlwpiis californicus (Stimpson), could at least in part be explained by a positive response which these commensals showed to their hosts. On the basis of these tests it was concluded that "certain echinoderm hosts produce a specific diffusible substance that acts as a powerful attractant for their commensals." Welsh (1930, 1931) had demonstrated that similar agents govern the specificity of certain clam-acarine partnerships. In the course of his work these chemical agents were found to be relatively stable. Boiling for five to ten minutes as well as putrefaction for a week at 37.5 C. had little effect on the material acting on the mites. Beyond this, no further investigation of the nature of the substance was carried out. To the writers it also seemed of primary importance to determine whether or not the attractants involved in echinoderm-annelid partnerships are stable, as a first step in an investigation of the nature of these substances. In addition, ques-tions had arisen as to the source of the attractants in the host. The necessity for investigation of the factors determining the specificity of further commensal partner-ships involving diverse phyla was, as always, present. In the summer of 1950, experiments designed to attack some of the above prob-lems were conducted at the Oceanographic Laboratories of the University of Wash-ington at Friday Harbor, under grants from the American Philosophical Society and the Society of Sigma Xi. The writers wish to express their appreciation to the Societies and to the Director and staff of the Laboratories for their generosity and assistance. THE GENUS ARCTONOE Material Evasterias and Stichopus with their attendant commensals were collected in the same localities and in the identical manner as described in earlier work (Daven-port, 1950). For one series of experiments, however, a large number of Evasterias averaging the size of a silver dollar (3-15 cm.) were collected on a point near the village of Olga on Orcas Island. These immature starfish did not seem to have as 71
BioStor
