Further Studies in the Behavior of Commensal Polychaetes

A new water-table test apparatus for the investigation of commensal response behavior is described. 2. Evidence is presented that the two populations of the facultative commensal Podarke pugettensis (Polychaeta: Hesionidae) which may be termed "commensal" and "free-living" differ markedly in their response to host animals, the commensal worms showing a strong tendency to respond positively to the host and the free-living worms not doing so. 3. Commensals with the starfish Luidia in Puget Sound appear to respond with almost equal intensity to other non-host animals (the response is not specific), while commensals of the star Patiria in Southern California show a more precise and specific response. This behavioral difference remains unexplained. 4. The behavior of three populations of the obligate commensal Arctonoë fragilis (Polychaeta: Polynoidae) was compared. Evidence is presented that each population (one commensal with the star Evasterias, one with the star Orthasterias and one with the star Solaster) shows a response to its host alone. 5. The response behavior of Arctonoë vittata (Polychaeta: Polynoidae), an obligate commensal of diverse habit, was investigated in relation to a number of its alternate hosts.