DORSIBRANCHIATA. 



375 



12. NEMATOIDEA or Thread-worms ; with a 



thread-like form ; no segments ; dense 

 covering ; straight alimentary canal ; as 

 Hair-worms, etc. 



13. KOTIFERA, minute forms with wheel-like 



appendages around the head. Referred 

 to the Crustacea by some naturalists. 



ANXULOIDA. 



J 



S.UB-SECTION II. 



THE ORDER OF DORSIBRANCHIATA OR LOB-WORMS, ETC. 



THE worms of this group belong to the sea. Some 

 species swim freely about, and others live in the sand or 

 mud. They get their name from the fact that, in general 

 they have the gills in the form of short branchial append- 

 ages along the back or body (Figs. 508-9), from the Latin 

 dor sum, the back, and Iragchia, gills. They are known 

 under the names of Sea-Centipedes or JSTereidae (Fig. 508) ; 

 Eunicidse a West Indian species of which (Eunice gi- 

 gantea) attains the length of four feet; " Sea Mice" or 

 Aphroditidse, which are more or less covered with silky 

 hairs of a brilliant metallic luster; and the Lob-worms or 

 Arenicolidaj, etc. Here also may be mentioned a re- 

 markable genus called Cirmtulus a new species of which 



FIG. 508. 



Sea-Centipede, tfereit, 



