Ciliophora 339 



commonly uniform except for the frequent occurrence of large cilia 

 around the cytostome. In some genera, however, somatic cilia are limited 

 to a few transverse bands or to one surface of the body. The cytostome 

 usually opens at the surface. There is no well defined oral groove or 

 peristome equipped with specialized cilia. Even if a rudimentary peri- 

 stome is present, or if there are distinct preoral and postoral fields of 

 cilia, the organization of the peristomial area is primitive as compared 

 with that in more specialized groups. There is often a circumoral zone 

 of cilia, somewhat longer and sometimes stouter than the somatic cilia. 

 In addition, the pharynx is commonly surrounded by a ring of rod-like 

 trichites, which are sometimes partially fused to form a pharyngeal basket. 



The position of the cytostome varies in different families and on this 

 basis, Kahl (100) has divided the suborder into three tribes. In one group 

 ("Tribe Prostomata") the cytostome is anterior. Among the families listed 

 below, this is the situation in the Actinobolinidae, Biitschliidae, Cole- 

 pidae, Didiniidae, Holophryidae, Metacystidae, and Spathidiidae. In a 

 second group ("Tribe Hypostomata") the cytostome lies on the flattened 

 ventral surface and in the anterior half of the body. This is the case in 

 the Chlamydodontidae, Dysteriidae, and Nassulidae. The cytostome of a 

 third group ("Tribe Pleurostomata") lies on a compressed margin of the 

 body — the narrow ventral surface, according to Kahl, although others 

 have considered the cytostome lateral in position. This is the condition 

 in the Amphibotrellidae, Amphileptidae, Loxodidae, and Tracheliidae. 



Family 1. Actiyiobolinidae. These prostomatous ciliates possess exten- 

 sible tentacles in addition to the usual ciliature. The tentacles in Dactylo- 

 chlamys pisciformis (103) are similar to those of many Suctorea (Fig. 7. 

 50, C). The tentacles in ActinoboUna vorax (221), which are slender struc- 

 tures emerging in the ciliary meridians (Fig. 7. 2, J), may be extended for 

 lengths of lOOpi or more, but are usually retracted is swimming ciliates. 

 The tip of each tentacle is said to contain a toxicyst (Chapter I). In 

 stained preparations the proximal ends of the tentacles are continuous 

 with a system of cytoplasmic fibrils (Fig. 7. 2, I). On the basis of such 

 tentacular equipment, Kahl (103) has suggested that the Actinobolinidae 

 are related to the ancestral holotrichs from which the Suctorea were 

 evolved and that Dactylochlamys may even represent a primitive type of 

 Suctorea which has not developed a sessile stage. 



Only three geneia have been assigned to the family: ActinoboUna Strand (103, 221; 

 Fig. 7. 2, I, J), Dactylochlamys Lauterborn (103; Fig. 7. 2, B), and Enchelyoniorpha Kahl 

 (103; Fig. 7. 2, A). ActinoboUna is the only genus in which a cytostome has been 

 described. The cytostome of A. vorax (221) opens into a pharynx surrounded by a 

 double ring of fibrils. These apparently converge in the rim of the cytostome (Fig. 

 7. 2, I). 



Family 2. Amphibotrellidae. This family contains the genus Amphi- 

 botrella R. and L. Grandori (106; Fig. 7. 2, K), characterized by location 



