DINOPHYCEAE 125 



DINOPHYCEAE 



Fig. 88 



This group is predominantly planktonic, naked forms being 

 most abundant in the sea, whilst in fresh waters one commonly 

 finds armoured forms which often have spiny processes that can be 

 regarded as adaptations to their pelagic existence. The majority of 

 the species are motile and characteristically possess two flagellae, 

 one directed forward and one transversely, both commonly lying in 

 grooves and emerging through pores. In one or two cases, however, 



Fig. 88. Dinophyceae. A, Peredinium anglicum, dorsal view. B, P. anglicum, 

 ventral view. C, Cystodinium lunare. D, Gymnodinium aeruginosum. E, Dino- 

 clonium Conradi. F, Gloeodinium montanum. a = apical plate, ac/) = accessory 

 plates, «2/) = antapical plates, ^ = girdle, w = nucleus, ^ = precingular plates, 

 ^c = postcingular plates, r = rhomboidal plate. (After Fritsch.) 



the flagellae may be situated anteriorly. In some forms ocelli^ 

 which are composed of a spherical lens and a pigment, can be ob- 

 served ; these are presumably connected with the perception of light 

 and they must be regarded as an elaborate development of the 

 ordinary red eye-spot. Two genera also possess nematocysts com- 

 parable to those found in hydroids. The numerous disk-like 

 chromatophores are dark yellow or brown in colour and sometimes 

 contain pyrenoids. There is one nucleus and the food reserve is 

 starch and fat, whilst the marine Dinoflagellates are noted for 

 possessing large vacuoles. Multiplication is by means of cell 



