472 



ANNELIDA. 



in the Cydippidae. Many are commensals, living in the tubes 

 of other worms, and in the ambulacral grooves of starfishes; this 

 is especially common with the Polynoids. A few are pelagic, e.g., 



Alciopidae, some 

 Pliyllodocidae, 

 Tomopteris, Typh- 

 loscolex, and some 

 sexual Nereids 

 and Syllids (He- 

 teronereids and 

 Heterosyllids). A 

 few are borers, 

 e.g., Polydora 

 ciliata in chalk, 

 limestone, shells, 

 etc., Sdbella saxi- 

 cava, etc. 



The majority 

 are littoral, but 

 they are found at 

 all depths to 3000 

 fathoms. They 

 either live freely, 

 creeping on the 

 bottom, or inhabit 

 tubes. The tube 

 is formed of 

 mucus which is 

 secreted by the 

 ventral gland- 

 shield, or other 

 glands. The mu- 

 cus hardens to 



form the tube, which may be strengthened by the incorporation of 

 mud, sand-grains, or pieces of shell, which are actively collected for 

 the purpose by the animal itself. In the Serpulids the tube is 

 fortified by the presence of calcareous matter secreted by the animal. 

 Some worms are phosphorescent, e.g., Chaetopterus, many Poly- 

 noids, Syllids, Terelellids, etc., and probably Tomopteris by special 

 organs on the parapodia, and PolyophtTialmus by the so-called 

 segmental eyes. 



FJG. 877. Part of a stock of Syllis ramosa (somewhat diagram- 

 matic, after Mclntosh, from Korschelt and Heider). d intestine 

 which branches through the entire stock. The stock is injured 

 in some places. 



