Flame bulb 



Trophi 



Excretory canal 



Ciliated feeding 

 apparatus 



^isj^-'.rm Mouth 



5^f|^gIlS^ Pharynx 



Gastric gland 



Esophagus 

 Stomach 



Vitelline gland 



Intestine 



— Cloaca 



Fig. 12.1. Class Rotifera. A 

 typical rotifer. Epiphanes senla; 

 semidiagrammatic. This is a 

 ventral view of a mature female. 

 (Redrawn, after various au- 

 thors, from C. G. Goodchild 

 in F. A. Brown, Jr., el a/.. 

 Selected Inverlebrale Types, copy- 

 right 1950 by John Wiley and 

 Sons, Inc., printed by per- 

 mission.) 



Cement gland 



Toes 



Pseudocoelomate Groups 

 THE PHYLUM ASCHELMINTHES 



The phylum Aschelminthes includes by all standards a mixed assemblage of 

 widely different forms. It is composed of six classes, of which the most 

 significant are the class Rotifera, or rotifers, and the class Nematoda, which 

 includes the most familiar examples of the so-called roundworms. The re- 

 maining groups are of such minor importance to the general student that they 

 need not be considered here. 



The Class Rotifera. The name Rotifera, or "wheel-bearers," is derived 

 from observations of these tiny animals by early microscopists, notably 

 Leeuwenhoek, who in 1703 described the form as bearing "two wheels thick 

 set with teeth as the wheel of a watch." This is particularly descriptive 

 of many species with anterior ciliated crowns; in the feeding activities of 

 these animals the cilia beat toward the mouth from both sides, and under low 

 magnification the cilia give the entirely erroneous impression of two tiny 

 wheels revolving in opposite directions. Rotifers are abundant in fresh water, 

 and there are also many marine species. All are microscopic in size, the 

 largest being about a millimeter in length. Rotifers are commonly free- 

 swimming animals, but they may become temporarily attached to the sub- 



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