178 



Aquatic Organisms 



Melicerta is a large sessile rotifer that lives attached 

 to the stems of water-plants and when undisturbed 

 protrudes its head from the open end of the tube, and 

 unfolds an enormous four-lobed crown of waving cilia. 

 It is a beautiful creature. Our picture shows the cases 

 of a number of Melicertas, aggregated together in a 



cluster, one case serving as a 

 support for the others. 



The crown of cilia about the 

 anterior end of the body is the 

 most characteristic structure 

 possessed by rotifers. It is 

 often circular, and the waving 

 cilia give it an aspect of rota- 

 tion, whence the group name. 

 It is developed in an extra- 

 ordinary variety of ways as 

 one may see by consulting in 

 any book on rotifers the figures 

 of such as Stephanoceros, Flos- 

 cularia, Synchceta, Trochos- 

 phccra and Brachionus. 



The cilia are used for driv- 

 ing food toward the mouth 

 that lies in their midst, and 

 for swimming. Most of the 

 forms are free-swimming, and 

 many alternately creep and 

 swim. 



Brachionus (fig. 87) shows 

 well the parts commonly found in rotifers. The body 

 is inclosed in a lorica or shell that is toothed in front 

 and angled behind. From its rear protrudes a long 

 wrinkled muscular "foot," with two short "toes" 

 at its tip. This serves for creeping. The lobed 

 crown of cilia occupies the front. Behind the quad- 



FlG. 86. Two clusters of rotifers 

 {Melicerta), the upper but 

 little magnified. Only the 

 cases (none of the animals) 

 appear in the photographs. 



