The Mastigophora 117 



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HE Mastigophora possess flagella at some stage of the life- 

 cycle, although many develop pseudopodia and show amoeboid activity. 

 The group may be divided into two classes, Phytomastigophorea and 

 Zoomastigophorea. 



CLASS 1. PHYTOMASTIGOPHOREA 



The phytoflagellates range from typical plants to forms whose 

 affinities with animals are more apparent, and some genera have even 

 occupied positions in both the Phytomastigophorea and the Zoomasti- 

 gophorea in different systematic treatises. The majority possess chroma- 

 tophores which contain chlorophyll, although the green color may be 

 masked to some extent by other pigments. The rest of the phytoflagellates 

 are colorless. Some differ from their pigmented homologues mainly in the 

 lack of chromatophores, and in certain instances, both colorless and pig- 

 mented species belong to the same genus. At the other extreme, certain 

 predominantly holozoic species have developed new organelles which 

 assist in feeding. 



Life-cycles may involve dimorphism, sometimes with alternation of 

 amoeboid and flagellate stages, or flagellate and palmella stages. Sexual 

 phenomena are well known in Phytomonadida and have been reported 

 occasionally in certain other orders (Chapter II). 



The Phytomastigophorea^ may be divided into the following orders: 



(1) Chrysumonadida: usually one or two flagella, sometimes three; typ- 

 ically with one or two, biu sometimes more chromatophores ranging from 

 golden-yellow to greenish-yellow or brown; a few genera lack chromato- 

 phores: no cytopharynx or "reservoir" is present; the cyst wall is typically 

 siliceous and contains a pore; encystment is endogenous; stored reserves 

 include leucosin and lipids, but no starch; many species are naked, some 

 secrete a lorica or test, others are enclosed in a membrane to which silice- 

 ous scales or calcareous elements (coccoliths) are added; the majority are 

 solitary, but some genera develop arboroid or spheroid colonies. 



(2) Heterochlorida: typically naked, with two unequal flagella; one 

 to a dozen or more chromatophores, pale yellow-green, or sometimes pale 

 yellow; no cytopharynx; reserves include leucosin and lipids, but no 

 starch; the cyst wall, which may contain two layers, lacks a pore; encyst- 

 ment is endogenous, as in Chrysomonadida. 



(3) Cryptomonadido: biflagellate; pellicle usually restricts changes in 



^ From the botanical standpoint, the Class Phytomastigophorea is a somewhat artifi- 

 cial arrangement of certain algal groups. As considered in the present chapter, the 

 Chrysomonadida represent part of the algal Class Chrysophyceae, the Phytomonadida 

 correspond to the Order Volvocales of the Class Chlorophyceae, and the Dinoflagellida 

 to the Class Dinophyceae. A modern discussion of the phytoflagellates as algae has been 

 published by Smith (260). 



