PHYLUM ROTIPERA 



189 



in motion they make the discs appear like rotating wheels 

 hence the name Rotifera (fero, I carry; rota, a wheel). 



These animals are remarkable for their small size. Though 

 they are well-developed metazoans with more special- 

 ized systems of organs than round-worms, they are usually 

 no larger than single-celled animals, and most species can 

 barely be seen with the naked eye. The mouth is situ- 

 ated between the trochal (ciliated) discs where it receives 

 the food brought in the vortex created by the cilia. The 

 food is ground in a mastax, or chewing stomach, which is 



FIG. 79. Rotifera. 



provided with chitinous teeth. Behind the mastax there 

 is a glandular stomach where digestion takes place, and the 

 residue passes out through an anus on the dorsal side near 

 the posterior end. The excretory system consists of a 

 pair of branched tubules and a contractile bladder which 

 empties through the anus. Rotifers have a body cavity, 

 but it is not a true ccelom. 



Rotifers are of separate sexes. The males are smaller than 

 the females and are often degenerate sometimes the 

 digestive system is entirely lacking. The females produce 

 two kinds of eggs: summer and winter. The summer eggs 

 are parthenogerietic, have thin shells, and are of two sizes 

 the larger producing females and the smaller males. The 



