DINOFLAGELLATA 311 



of planktonic forms possess a large number of small chromatophores 

 which are usually dark yellow, brown or sometimes slightly greenish 

 and are located in the periphery of the body, while bottom-dwelling 

 and parasitic forms are, as a rule, colorless, because of the absence of 

 chromatophores. A few forms contain haematochrome. The method 

 of nutrition is holophytic, holozoic, saprozoic, or mixotrophic. In 

 holophytic forms, anabolic products are starch, oil, or fats. 



Anterior flagellar pore n. /" -\ -Epicone 



}■£ \ ^Transverse flagellum 



Annulus or girdle - — Ls^^^^^^^ 



^C \\ 4 Sulcus 



Hypocone V— ][r^>j/ 



Longitudinal flagellum - — j ^Posterior flagellar pore 



Fig. 125. Diagram of a typical naked dinoflagellate (Lebour). 



Asexual reproduction is hy binary or multiple fission or budding 

 in either the active or the resting stage and differs among different 

 groups. Encystment is of common occurrence. In some forms the 

 cyst wall is formed within the test. The cysts remain alive for many 

 years; for example, Ceratium cysts were found to retain their vital- 

 ity in one instance for six and one-half years. Conjugation and sexual 

 fusion have been reported in certain forms, but definite knowledge on 

 sexual reproduction awaits further investigation. 



The dinoflagellates are abundant in the plankton of the sea and 

 play an important part in the economy of marine life as a whole. A 

 number of parasitic forms are also known. Their hosts include vari- 

 ous diatoms, copepods and several pelagic animals. 



Some dinoflagellates inhabiting various seas multiply suddenly in 

 enormous numbers within certain areas, and bring about distinct 

 discolorations of water, often referred to as "red tide" or "red wa- 

 ter." Occasionally the red water causes the death of a large number 

 of fishes and of various invertebrates. According to Galtsoff (1948, 

 1949), the red water which appeared on the west coast of Florida 

 in 1946 and 1947, was due to the presence of an enormous number 

 of Gymnodinium brevis and this dinoflagellate seemed in some man- 

 ner to have been closely correlated with the fatal effect on animals 

 entering the discolored water. Ketchum and Keen (1948) found the 

 total phosphorus content of the water containing dense Gymnodin- 

 ium populations to be 2.5 to 10 times the maximum expected in 



