CHAPTER XXX 



ORDER 3 OLIGOTRICHIDA BUTSCHLI 



THE CILIA are greatly reduced in number in the Oligotrichida. 

 The adoral zone which is invariably present, is a complete 

 ring bordering the left-side margin of the peristome which is at 

 right angles to the main body axis. The Oligotrichida are 

 chiefly parasitic forms. 



The order is divided into two families as follows: 



Free-living small forms Family 1 Halteriidae 



Parasitic in the digestive tract of mammals. . . .Family 2 Ophryoscolecidae 



Family 1 Halteriidae Claus 



Genus Halteria Dujardin. Small spherical body. Adoral 

 zone at the anterior end. Near the middle of the body there is a 

 circle of long cirri which serve for springing movement. No 

 other cilia. Macronucleus spherical or oval; a single contrac- 

 tile vacuole. Fresh water. 



Halteria grandinella Miiller (Fig. 164, a). Body length 20 

 to 30 microns. Common in infusion, pond, and stagnant water. 



Genus Strombidium Claparede and Lachmann. Similar to 

 Halteria, but without springing cirri. Sometimes yellowish in 

 color. The adoral zone is protrusible; frequently with tricho- 

 cysts. A single cilium or a few cilia may be present on the vent- 

 ral side. Salt or fresh water, 



Strombidium typicum (Lankester) (Fig. 164, b). About 35 

 microns in length. Marine. 



Family 2 Ophryoscolecidae Claus 



Genus Ophryoscolex Stein. In the stomach of ruminants. 

 Body more or less pyriform. Posterior end is drawn out into a 

 number of processes; at the anterior end there is a conspicuous 

 ring of cirri which continues through the cytostome into the 

 cytopharynx. A little toward the back there is an incomplete 

 circle of cirri. With numerous contractile vacuoles. 



[3811 



