Ciliophora 381 



plate of each membranelle usually contains two rows of basal granules, 

 although three rows (rarely, four) may be present (104). The group may 

 be divided into six suborders. 



Suborders of the Spirotrichida 



Suborder I. Heterotrichina. Somatic ciliation is usually complete. How- 

 ever, the dorsal surface may be sparsely ciliated in some families and 

 shows more extensive reduction of ciliation in exceptional cases. The 

 peristome, usually elongated and fairly narrow, bears the adoral zone 

 of membranelles along the left wall. In addition, an undulating mem- 

 brane often extends for some distance along the right margin. 



Suborder 2. Oligotrichina. Although the adoral membranelles are well 

 developed, there is a marked reduction in somatic ciliation and the peri- 

 stomial field, around which the adoral zone extends, is free from cilia. 

 An undulating membrane lies at the right margin of the adoral area in 

 certain genera. 



Suborder 3. Tintinnina. These ciliates, sometimes grouped with the 

 Oligotrichina, are typically conical forms with a lorica. The adoral zone 

 of membranelles follows a spiral course on the flattened oral pole. 



Suborder 4. Entodiniomorphina. This group, sometimes placed in the 

 Oligotrichina, includes parasites of the rumen and intestine of herbivores. 

 The ciliation may be limited to the adoral zone or there may be one or 

 more additional bands or gioups of membranelles. 



Suborder 5. Hypotrichina. The somatic cilia are replaced by cirri which 

 are generally distributed in particular fields and limited essentially to the 

 ventral surface. 



Suborder 6. Ctenostomina. These are laterally compressed, wedge- 

 shaped ciliates with a rigid pellicle decorated with longitudinal ribs. The 

 body is sparsely ciliated, and the peristome is a pouch containing an 

 adoral zone of eight membranelles. 



Suborder 1. Heterotrichina 



Since the somatic ciliation is practically complete in the majority, these 

 ciliates are usually considered the most primitive Spirotrichida. However, 

 there is a trend toward reduction of the dorsal ciliature in some genera, 

 and the Peritromidae are ciliated only on the ventral surface. In addition 

 to the adoral zone of membranelles on the left, there is often an undulat- 

 ing membrane at the right of the peristome. This membrane is sometimes 

 replaced by a double row of heavy cilia. Thirteen families have been 

 recognized. 



Family 1. Balantidiidae. This family includes Balantidiiun Claparede 

 and Lachmann (130, 139, 174, 214; Fig. 7. 29, A-E), represented by para- 

 sites of the digestive tract in both vertebrates and invertebrates. Somatic 

 ciliation is complete and the cilia are arranged in approximately longi- 



