PHYLUM ANNELIDA 



CLASS CH^TOPODA 



The Chaetopoda include various forms of worms. The 

 body is segmented and generally the segments are similar. 

 There is a ventral nerve-cord and a nerve-ring round 

 the oesophagus connected with a pair of ganglia above it. 

 A vascular system and a body-cavity (ccelom) are present. 

 The Chaetopoda possess bristle-like processes termed setae 

 which assist in locomotion. There are three orders, (1) the 

 Archiannelida, e.g. Polygordius, (2) the Oligochaeta, e.g. 

 the common earthworm Lumbricus, and (3) the Polychaeta. 

 The Archiannelida and the Oligochaeta are unknown in 

 the fossil state. The Hirudinea or leeches are regarded 

 by some writers as a distinct Class of the Annelida, but 

 by others as a division of the Chaetopoda; they do not 

 occur fossil. 



ORDER III. POLYCH^TA 



The members of this Order are nearly all marine ; 

 they are characterised by the possession of numerous setae, 

 which are placed on special processes termed parapodia. 

 Tentacles are usually present on the head. Many forms 

 live in tubes, which may consist of carbonate of lime, of 

 chitinous material, or of grains of sand cemented together 

 by a secretion. On account of the possession of this tube 



