OTHER ANNELIDS 119 



Notice the eyes, tentacles, and jaws on the head, and the pair of 

 paddlelike appendages, the parapodia, on each somite. What differ- 

 ences in habits do these organs suggest, as compared with the earth- 

 worm? It is probable that the latter has descended from ancestors 

 having greater external specialization and thus more like Nereis. 

 What habits of earthworms may be related to such degeneration? 



(c) There are also many marine forms that are specialized for 

 living in tubes or burrows and feeding in various ways. Serpula 

 {Hydroides), with its brilliantly colored tentacles, and Chaetopterus, 

 with its parchmentlike tube, are examples. The leeches of fresh water 

 and moist soil are representative of another group of annelids. 



