PHYLUM ANNELIDA 



195 



fresh-water, and terrestrial forms; and they all possess setae (chaetae), 

 or bristlelike appendages on the body segments. The setae are 

 chitinous and are embedded in pits of the integument. They bear 

 muscle attachments which make them movable and therefore useful 

 in locomotion. The coelom, which surrounds the straight digestive 

 tract, is divided between the segments by partitions known as septae. 



Fig. 99. — Representative annelids. From left to right, Arenicola cristata, lug 

 worm ; Amphitrite ornata, marine annelid with branching gills ; Hirudo medicinalis , 

 large medicinal leech (upper center) ; Aphrodita ornata, sea mouse (lower center) ; 

 Nereis vii-ens, sand worm or clam worm ; Lumb7-icus terrestris , earthworm or angle- 

 worm. (Courtesy of Denoj-er-Geppert Company.) 



Typically, each coelomic space possesses a pair of nephridial tubules 

 which communicate with the coelom at one end by means of a ciliated, 

 funnellike opening, the nephrostome. The other end opens to the out- 

 side by means of a nephridiopore. The nephridia remove nitrogenous 

 waste materials from the coelomic cavities and from the blood. 



