CHAPTEE X 



CHAETOPODA" 



fArchiannelida. 



r Naidomorpha — Nais, Chaetogaster. 

 oi i T J Oligoohaeta-! Lumbricomorpha — Lwmbricus, Megascolides, 

 Chaetopoda-^ ( Eudrilus, Perichaeta. 



p 1 T, + / Errantia — Nereis, Aphrodite, Eumke, Tomopteris. 

 I^roiyonaeta | SedenUriek—Arenicola, Sabella, Gapitella. 



it \ 



ll 



Chaeacteeistics. — Segmented animals, with a more or less pro- 

 miTient prostomiwm or region in front of the mouth. Loco- 

 motion effected hy cilia, or ly setae implanted in the "body 

 wall or home hy lateral processes of the hody termed para- 

 podia. Each seta is the product of a single cell. The 

 segments are divided externally ly grooves, internally hy septa. 

 A pair of nephridia are typically found in each segment. 

 The Chaetopoda are divided into three sub-classes : the 



Aechiannelida, the Oligoohaeta, and the Polyohaeta. 



archiannelida. 



Characteristios. — Marine worms with small prostomium. The 



segmentation of the hody is externally marked hy rings of 



ciliated cells, and hy slight grooves. There are no setae or 



parapodia or hranchiae, hut the head hears one or more pairs 



of tentacles. The longitudinal muscles are in four hands. 



The nervous system retains its connection with the hypodermis 



throughout life. The head hears a pair of ciliated grooves. 



The Archiannelida comprise a group of minute marine 



animals, which are to some extent intermediate between the 



Turbellarians and the Chaetopoda. The group includes four 



genera : Polygordius, Protodrilus, Histriodrilus, formerly known 



as Histriohdella and classified with the leeches, and Dinophilus. 



