SUB-CLASS: PHYTOMASTIGINA 



277 



There are two flagella, one of which usually lies in a groove in the thick 

 covering of the body. Chromatophores may or may not be present. There 

 are a large number of genera, of which Ceratium, Gymnodinium, Diplo- 

 dinium, and Goniodoma are representatives (Figs. 125, 126). 



Fig. 126. — Gymnodinium rhomboides (1 and 2), and G. spirale (3) (xca. 1,000). 

 (From Oltmann, 1922, after Schutt.) 

 qf. Equatorial groove ; If, longitudinal groove. 



4. Order: EUGLENOIDIDA. 



Large forms covered with a definite periplast often longitudinally 

 marked. The shape of the body may be permanent or it may change 

 according to the rigidity of the periplast. At the anterior end of the 

 body is a depression, in which the flagellum arises. Sometimes there 

 are two flagella. In some forms a cytostome leading to an oesophagus 

 occurs in the anterior depression. There is a characteristic system of 

 excretory vacuoles, consisting of a reservoir into which discharge one or 

 more contractile vacuoles. A red pigment spot, the stigma, is often found 

 at the anterior end of the body, while green chromatophores are fre- 

 quently seen in the cytoplasm. The order ( = Euglenoidina Biitschli, 1884) 

 includes well-known genera such as Euglena (Figs. 6 and 128, B), Astasia 

 (Fig. 127), and Phacus (Fig. 128, A), and the coprozoic Copromonas (Fig. 133). 



5. Order: PHYTOMONADIDA. 



These forms, which are often considered to be unicellular algae, possess 

 definite cellulose walls and are devoid of cytostome. There are usually two 

 flagella, which emerge through a pore in the cell wall. Green chromato- 

 phores often occur, while some are coloured red by a pigment known 

 as hsematochrome. Eed-pigmented stigmata are not infrequently present. 

 Colonial grouping of a varying number of individuals is a common feature, 

 while there may be a complicated life-history, in which syngamy is 

 associated with the production of differentiated male and female gametes 



