258 



BIOLOGY OF THE PROTOZOA 



are symbiotic as in the yellow cells of Radiolaria and Foraminifera 

 (Zooxanthelhe especially ChrysldeUa). Some are also ectoparasitic 

 on diatoms, filamentous algte and Crustacea; others are endopara- 

 sitic in water-dwelling animals such as Gammarus and allied 

 Crustacea, and on rotifers. 



Order I. CHRYSOMONADIDA. 



The Chrysomonads are characterized b\' the presence of yellow- 

 brown chromatophores ; by the presence of oils and highly ref ractile 

 granules (leucosin) ; by spore formation in cysts and by the silicious 

 composition of the cyst walls. Starch is absent. The chemical 

 nature of the coloring matters is not yet satisfactorily made out. 

 For Chromidina rosanoffii, Pascher (1913) states that chrysochloro- 

 phyll, phytochrysin, and chrysoxanthophyll have been identified 

 although whether or i^ot identical with similar chromophyll sub- 

 stances in higher plants is unknown. 



,%f-!kS«e 





A 



B 



Fig. 125. — Typos of Chry8omoiiadida. .4, B, motile and Palmella stages of Chrom- 

 ulina flavicans. (From Calkins after Biitschli.) C, Mallomonas plcesslii. (From 

 Dofiein after Klebs.) 



The flagella are always inserted apically and are one or two in 

 number, the number and relative sizes determining some of the 

 families. The monads are comparatively simple in structure and 

 the body is usually regular and without dor so-ventral differentia- 

 tion. The pellicle is usually delicate and inconspicuous but may be 

 heavy and provided with keels, ridges, flanges, etc., or covered by 

 fine silicious plates as in Mallomonas (Fig. 125). Cups and houses 

 of cellulose, often colored by iron oxide, are abundant and frequently 



