POLYCHAETA 



239 



ments which have a notopodium with capillary setae and a neuro- 

 podial ridge with chaetae resembling uncini (crotchets); the median, 



ac/i. per. ^^^. 



m.r.{ 



Fig. 178. Arenicola marina. Side view. After Ashworth. phar. pharynx; 

 pr. prostomium; per. peristomium; ach. ist achaetous segment; a.r. anterior 

 region; m.r. median region; p.r. posterior region; not. notopodium; neur. 

 neuropodium. 



the segments of which have gills in addition ; and the posterior, in 

 which parapodia and chaetae are entirely lost. 



