2. Cells inclosed in a brown or buff-colored shell or test of various 



shapes, with a flagellum aperture Trachelomonas 



2. Cells free-living, not inclosed in a test 3 



3. Cells much flattened dorsiventrally, usually spirally twisted 



in at least a part of the cell Phacus 



3. Cells not flattened, round or ovoid in cross section 4 



4. Cells fusiform, cylindrical, or elongate-fusiform, round 



or nearly so in cross section ( rarely slightly flattened ) Euglena 



4. Cells broadly ovoid or pyriform, usually furnished with a short 

 caudus; paramylon bodies 2 very large and conspicuous 

 lateral rings or plates Lepocinclis 



EUGLENA Ehrenberg 1838, p. 104 



Cells mostly free-swimming, rarely creeping; fusiform, cylindrical, 

 or ovate, usually round in cross section but rarely slightly flattened; 

 the posterior end either rounded or produced, sometimes extending 

 into a fine point or caudus, the anterior end usually narrowed and 

 sometimes conspicuously 2-lipped; periplast either firm, giving the 

 cell a rigid shape, or soft and pliable, the cell metabolic and con- 

 stantly changing shape in its movements; when firm, the periplast 

 decorated with fine spiral striations or rows of granules; a gullet and 

 a reservoir in the anterior end from which arises a single flagellum of 

 variable length; chloroplasts variable, either numerous ovoid discs, a 

 few ribbon-like bands, or, rarely, star-shaped plates, sometimes with 

 pyrenoids, which are embedded in the chloroplast and protrude 

 from either side; chlorophyll sometimes masked by an abundance 

 of brick-red or blood-red haematochrome, usually only temporarily 

 present and incident to intense illumination; food reserve paramylon 

 in the form of a few large or numerous small rods, plates, rings, or 

 discs. 



There are many species of Euglena, differentiated and identified 

 by the shape of the cell, the periplast markings, the form of the 

 chloroplasts, the shape and arrangement of the paramylon grains, 

 and the presence or absence of pyrenoids. Considerable discrimina- 

 tion in taxonomic determinations is required, therefore, and because 

 important characteristics are often obscure, identification is not easy. 



While some species of Euglena appear not uncommonly in the 

 euplankton, most are found in the tychoplankton, in the shallow 

 water of quiet bays, in ponds and ditches. A few species seem to be 

 confined to acid water, and in Sphagnum bogs they may form a 

 conspicuous green film over submerged or partly submerged mosses. 

 In small ponds and sloughs a heavy surface bloom may develop so 

 that a green film is produced. A pond often appears brick-red be- 

 cause of the production of haematochrome in the cells when exposed 

 to intense light. 



[389] 



