Chap. 27 AN AQUATIC MISCELLANY 539 



worms, the body cavity has no special lining and hence is not a coelom. 

 Rotifers are composed of relatively few cells, commonly a definite number 

 characteristic of a species. Many of the adults are shaped like larval worms 

 (trochophores). 



Unique Features. The corona is unique and essential in the life of rotifers 

 (Fig. 27.6). It is an irregular disk rimmed and banded with cilia whose beat 

 creates the effect of rotation, the wheels that delighted Leeuwenhoek. The 

 corona functions in locomotion, in gathering food, and in respiration. The 

 mastax or chewing pharynx is unique. In other animals food is ground after it 

 leaves the mouth, in the gizzard (part of the esophagus) of the grasshopper, 

 and in the stomach of lobsters, but only the rotifers have a chewing-throat. 



Structures and Functions. Various rotifers are excessively slender, almost 

 spherical, turtle-shaped, and flowerlike; very many of them have figures with 

 profiles like those of carrots and turnips (Fig. 27.5). The anterior end is 

 topped by the corona. At the posterior end, the body narrows into the foot and 

 one or two toes. Rotifers can poise and pirouette with sure stance because in 

 each toe there is a cement gland that secretes a sticky temporary anchorage. 



Numbers of Cells and Nuclel There is probably an approximately con- 

 stant number of cells in the bodies of various species of multicellular animals, 



VENTRAL 



Corona 



Mostax 



Salivary gland 



Gastric gland 

 Ovary 



Yolk gland 



Excretory 

 bladder 

 Pedal gland 



Toe 



Corona 

 Mostox 



Stonnach 

 Neohridio 



Intestine 



DORSAL 



Fig. 27.6. General structure of a female rotifer. The majority of rotifers are 

 females; in many species males are unknown and reproduction is altogether 

 parthenogenetic. Unique features of rotifers are the corona or rotating crown of 

 cilia, and the mastax or chewing pharynx. (Courtesy, Robert W. Pennak: Fresh- 

 water Invertebrates of the United States. Copyright 1953, The Ronald Press 

 Company.) 



