308 Animal Biology 



Example: Polygordius (about two inches long, and internally resembles the 

 earthworm). 



Class 2 — Chaetopoda (ke-top'oda) (Gr. chaite, bristle; pons, appendage). 

 — Terrestrial, marine, or fresh-water annelids possessing chitinous bristlelike setae 

 (chaetae) embedded in pits of the integument and moved by means of attached 

 muscles. The coelom is divided by numerous intersegmental septa (partitions). 



f ye 6pobs 

 -Cerebral qana]]a 

 Nerve rincj 



Head--. 



Pharynx 



/-^e Diverticulum (crop) 



_ Ventral nerve cord 

 Lateral blood vessels 



Anterior and posterior 

 Sachers 



Jtomach H _ 



U^Divertkulum (crop) -\_ 



Rectum 



Anus. 



Fig. 114. — Common leech of the class Hirudinea, phylum Annelida, dissected 

 from the dorsal side to show the nervous and circulatory systems, A, and the 

 digestive system, B. The anterior and posterior suckers of the ventral side are 

 shown separately. 



Order 1 — Polychaeta (pol i -ke' ta) (Gr. poly, many; chaeta, hrisiles) . 

 — Marine types with many setae situated on flat, fleshy lateral outgrowths known 

 as parapodia (used for locomotion and respiration). These worms usually have a 

 well-developed head bearing appendages. The sexes are separate. There is a 

 free-swimming, ciliated larval stage known as a trochophore (Gr. trochos, wheel; 

 phoreo, to bear). 



Example: Sandworm (Clamworm) (Fig. 113). 



Order 2 — Oligochaeta (ol i go -ke' ta) (Gr. oligo, few; chaeta, 

 bristles). — This order consists mostly of terrestrial and fresh-water annelids with 

 few setae, no parapodia, and no distinct head with appendages. Both sexes are 



