220 University of California Publications in Zoology [Vol. is 



the size of the body. Comineiisals that live on the surface of moving 

 animals have the same advantage. While the food is not carried 

 directly to their mouths, the polynoid however is carried to new feed- 

 ing grounds and no energy is used in locomotion. Hence there is less 

 chance for reduction of the size of the body. Moreover, the polynoid 

 may become an ectoparasite, obtaining some of its food directly from 

 its messmate. It has been found that some Polynoidae living on 

 sponges had in their digestive tracts spicules of the sponges on which 

 they lived. This proves that they are feeding on their hosts. They 

 may become ectoparasites on other animals in a similar manner, con- 

 suming some of the secretions or part of the food of their hosts. 



Another interesting feature is the adaptive coloration in Poly- 

 noidae. This evidently is the result of the environment. Such an 

 example remarkable for its adaptive coloration is Polynoe pulckra. 

 The worm is commensal with two animals, the sea cucumber, Holo- 

 thuria californica, and the keyhole limpet, Lncapina vrenulata. Liv- 

 ing specimens from both hosts were given to me for identification. 

 Judging from the color they look more like different species than indi- 

 viduals of the same species. Only microscopical examination reveals 

 the identical specific characteristics of both. The example living on 

 the holothurian mimics the color of the latter to perfection and can be 

 hardly detected when it lies quietly on the surface of its host. The 

 polynoids occupying the cavity between the mantle flap and the foot 

 of the limpet are very conspicuously colored, with prominent black 

 markings which show i:)lainly against the uniformly colored, whitish 

 yellow background of the ventral surface of the limpet. 



Another example of a polynoid showing great adaptive coloration 

 is Polynoe fragilis. This species lives in the ambulacral groove of the 

 starfish, Asterias ochracea and Astenas trochelii. Johnson (1897) 

 had an opportunity to observe the polynoid on the aboral side of the 

 starfish where its coloration harmonized so well with that of the 

 Asterias that it escaped any notice. The elytra of this polynoid also 

 are thin and delicate, wdthout any tubercles or prominences, and cov- 

 ering the dorsum only partly ( pi. 8, fig. 32 ) . A remarkable adapta- 

 tion is also seen in the setae (pi. 7, fig. 14). The latter are few, 

 slender, pointed and hooked, being thus well adapted for attachment. 

 Moreover, the setae as they become blunt from wear are continually 

 replaced by new pointed ones growing out from the base of the para- 

 podia (pi. 7, fig. 15). The latter characteristic is not common to all 

 Polynoidae but is an exception observed in a few species which are in 

 a habit of attaching themselves to other animals. 



