Survey of the Animal Kingdom 299 



Classification of the Phylum Trochelminthes (Rotifera)* (Fig. 102) 



In the classification of the rotifers, the following characteristics are used: (1) 

 the presence of one or a pair of ovaries; (2) whether males are usually present 

 but degenerate; males unknown; or males fully developed; (3) absence or pres- 

 ence of lateral antennae on the body. If desired, the student is referred to a 

 more complete classification in other books. 



CiUa 



Mouth . ^^£ 



MastaK 



(jasttic <j1ar)d -. . 



Excretory canal 



Bladder 



Intestine 



Cloacal opening _ 



Toot 



Flame cell 



Brain 



Esophaqus 



Stomach 



Ovary 



Oviduct 



^Pedal glands 



Fig. 102. — A female rotifer (much enlarged) of the phylum Trochelminthes 



(Rotifera). 



Phylum 8. Echinodermata (e ki no -dur' ma ta) (Gr. echinos, spiny; dermos, skin 

 or covering) 



General Characteristics 



The echinoderms have a spiny skeleton of calcareous plates which usually 

 covers the body. The adults have radial symmetry with five antimeres (divisions 

 of a radially symmetrical animal). The larvae have bilateral symmetry. The 

 adult animals are triploblastic, having three primary germ layers: ectoderm, 

 mesoderm, and entoderm. An anus is usually present. The coelom (body cavity) 

 is well developed. The type of locomotion which is peculiar to many types of 

 echinoderms is accomplished by tube feet. These are branches of the water 

 vascular system which is a division of the coelom. All echinoderms are marine. 

 Many species have great powers of regeneration, particularly after autotomy (Gr. 



*Sometiines the term Rotifera is used as a class under the phylum Trofhelminthes, 



