PROTOPHYTA 



67 



and processes and frequently give rise to fantastic shapes 

 (Fig. 33). 



These organisms are unique in having a characteristic groove 

 (annulus), which usually encircles the cell. It is present in both 

 naked and shelled forms and provides a furrow in which lies 

 one of the two flagella (Fig. 34). This furrow is sometimes at 

 the extreme end of the cell but in others it apparently disappears 

 entirely, leaving the encircling flagellum free in the water (Ex- 



rig. 34— GONYAULAX 

 APICULATA 



A common fresh-water dinophyceae 

 with characteristic furrow running 

 about the body. There are two fla- 

 gella: one. F, occupies the transverse 

 furrow, the other, FF, extends out 

 into the water 



From a photomicrograph by the author 



Magnification, 600 r/ 



uviaella). The second flagellum is more thread-like and vibrates 

 freely in water. 



Chromatophores of green, yellow, or brown color, and vary- 

 ing in number from two large bodies to many small disk-shaped 

 structures, may be present, but are absent here and there in repre- 

 sentatives of all families of the group and in all of the deep-sea 

 forms. The type of food-getting varies accordingly, from a 

 strictly plant type (holophytic) to a strictly animal type (holo- 

 zoic), although there are some remarkable adaptations to a para- 

 sitic mode of life (Blastodiniaceae) , a most extreme case being 

 that of Haplozoon (Fig. 24, page 53), a parasite found in the 

 intestines of marine worms. In this form there is a return to the 

 filamentous type of algae. 



Reproduction is effected by division of the cells into two, 

 usually along the longitudinal axis. In Ceratium hirundinella the 

 complex shell splits between definite plates, the protoplasm di- 



