50 PROTOZOA 



Key to the subclasses of Infusoria: 



Oj Cilia present 1. CILIATA 



o 2 No cilia present in the adult, but long sucking tubes 2. SUCTOEIA 



SUBCLASS 1. CILIATA. 



Protozoa with cilia and usually with a definite mouth and gullet: 

 4 orders with about 1,000 species, of which about 400 are marine. 

 Key to the orders of Ciliata: 



a t Cilia usually, but not always, present on all parts of the body. 



&! Cilia all approximately of the same length 1. HOLOTRICHIDA 



6 2 Mouth surrounded by an adoral zone of large cilia 2. HETEROTRICHIDA 



2 Cilia present on only a part of the body. 



&! Cilia confined to the ventral side 3. HYPOTRICHIDA 



6 2 Cilia confined to one or more rings around the body 4. PERITRICHIDA 



ORDER 1. HOLOTRICHIDA. 



Protozoa in which the cilia are usually evenly distributed over the 

 body, with a tendency to arrange themselves in straight lines, which 

 have often a spiral arrangement; in the vicinity of the mouth the cilia 

 are often longer than elsewhere and in a few forms are confined to this 

 region; trichocysts almost always present: 10 families. 



Key to the families of Holotrichida here described : 



Ot Animals not parasitic. 



&! Mouth closed except when taking in food, and without undulating membrane. 

 G! Mouth terminal or subterminal. 



d^ Body usually oval or cylindrical 1. ENCHELINIDAE 



d 2 Dorsal side arched ; forward end often neck-like 2. TRACHELINIDAE 



c 2 Body ovoid ; mouth in middle or posterior region .... 3. CHLAMYDODONTIDAE 

 Z> 2 Mouth always open and ventral with an undulating membrane around it or 



in the gullet. 

 c x Oral groove absent or slightly developed. 



di No equatorial zone of cilia 4. CHILIFERIDAE 



d 2 Broad equatorial zone of cilia 5. UP.OCENTRIDAE 



c 2 Long oral groove present. 



d t No undulating membrane along oral groove 6. PARAMECIIDAE 



d 2 An undulating membrane along the oral groove 7. PLEURONEMIDAE 



o 2 Animals parasitic ; mouth absent 8. OPALINIDAE 



FAMILY 1. ENCHELINIDAE. 



Usually oval Infusoria, sometimes with a long slender forward por- 

 tion, with a terminal mouth by which large objects are swallowed, food 

 not being introduced in currents, as the gullet is never ciliated: about 

 18 genera; principally in fresh water. 



