191^] Esseubcrg: Distribution of the Polyncndae 211 



Smaller and weaker polynoids are usually devoured by their stronger 

 companions. They also feed on other annelids, small crustaceans, 

 raollusks, sponges, and other small animals, as well as diatoms which 

 are often swallowed with the debris. Some species living as com- 

 mensals become ectoparasites, feeding on their messmates. 



In connection with their food habits it is interesting to observe the 

 modes of self defense or protection among the different species of 

 Polynoidae, as well as among other annelids. The Polynoidae naturally 

 hide beneath pebbles, empty mollusk shells or weeds in the aquarium. 

 Halosydna calif ornica when disturbed or attacked by individuals of its 

 own kind moves away quickly but without any wriggling motions, 

 very often leaving behind the attacked posterior segments or elytra. 

 Some other Polynoidae act in the same manner. Harmothoe, on the 

 other hand, when disturbed moves very swiftly with a vibrating, 

 wriggling motion at first and then coils up, turning its ventral surface 

 inside of the ring and spreading out its spiny, rough scales and its 

 numerous serrated setae in such a manner as to protect the body. 

 Harmothoe imbricata and HarmotJioe liirsuta have been observed to 

 use this mode of self defense. It seems as if the creatures knew 

 instinctively the value of their protective organs and how to use them 

 to the best advantage. 



Other annelids that lack defensive organs such as chitinous jaws 

 and rough elytra have other means of self protection. If Nephthy- 

 didae, Nemertidae, or Phyllodocidae are attacked by other annelids or 

 are disturbed in some other way, they immediately protrude the pro- 

 boscis, extruding a slimy substance which evidently must be disagree- 

 able to their aggressors, for the latter immediately withdraw. 



The abundance or scarcity of food undoubtedly plays an important 

 role in the distribution of polynoids, so that one would naturally expect 

 to find the worms more abundantly represented in localities Avhere the 

 food is at the maximum. The constitution of the bottom may deter- 

 mine the annelid population. It has been observed that some Poly- 

 noidae, and Annelida in general, occur in a depth of 14 fathoms in 

 Kiel Bay, while the same species are found off the Faroes in 60 to 100 

 fathoms. Again, some species occur in great abundance on the shores 

 of Greenland and Denmark at a depth of 6 to 10 fathoms, while around 

 the Faroes they are only scantily represented at a depth of 60 fathoms. 

 The cause of this difference in bathymetric distribution has been attri- 

 buted to the differences in the constitution of the bottom. The shores 

 of the Faroe Islands are rocky and steep, and the soft, muddy bottom 



