34 INVERTEBRATE ZOOLOGY 



exclusively marine and in this group is now included the large 

 Noctiluca noted for its phosphorescence. Most of the Volvox 

 family are limited to fresh water where they occur as conspicuous 

 elements of the plankton, frequently so abundant as to impart 

 distinctive colors, odors, and tastes to the water. One family 

 includes species, especially of the genus Chrysidella, which live 

 symbiotically within the bodies of other animals and are the 

 "yellow cells" of the Radiolaria and Foraminifera. While some 

 members of this subclass live as parasites on or in other animals, 

 most of the hosts are invertebrates, and hence as parasites they 

 have been relatively unimportant and have received little 

 attention. 



Subclass ZOOMASTIGINA 



The Zoomastigina include the orders of flagellates the members 

 of which are distinctly animal in their nutrition or receive their 

 food by absorption. Hence in food habits they are classed as 

 holozoic and saprozoic. Chlorophyll and chromatophores, so 

 characteristic of the Phytomastigina, are lacking in this subclass, 

 consequently the autotrophic method of nutrition is lacking. 

 The kinetic and locomotor elements are very highly specialized 

 especially in the parasitic forms. Colony formation is common, 

 particularly the arboroid type. There are no instances in which 

 fertilization is definitely known. Fission may occur in either a 

 free-swimming or an encysted state, and multiple fission may 

 result in the formation of a number of individuals within the 

 membrane of the original cell. Encystment is practically 

 universal. 



Some of the most important members of the Mastigophora 

 belong here because of the prevalence of the parasitic habit in the 

 Protomastigina. Four orders are recognized in this classification, 

 though authorities differ in the number and grouping of the forms 

 within this subclass. The orders are not clearly defined units 

 but some probably represent groups of convenience. 



The simplest members of this subclass show confusing mixtures 

 of flagellate and rhizopod characters, for forms like Mastigamoeba 

 and Mastigella (Fig. 15) possess numerous pseudopodia and a 

 permanent flagellum. 



The minute monads and the colonial Anthophysa are frequently 

 encountered in laboratory cultures. A delicate collar surrounds 

 the base of the flagellum in the choanoflagellates in such close 



