The Mastigophora 141 



is a large ovoid stage, attached by means of a hold-fast to the gill-fila- 

 ments of a marine fish. At maturity, the parasite drops off the host, 

 the hold-fast is retracted, and the corresponding gap in the cellulose- 

 membrane is closed. Fission then results in many gymnodinioid flagel- 

 lates which seek a new host (26, 199). 



The Dinoflagellida may be divided into five suborders: Prorocentrina, 

 with a bivalve theca but no distinct girdle or sulcus; Gymnodinina, 



Fig. 4. 19. A-C. Amyloodinium ocellatum, X475 (after Nigrelli); para- 

 sitic stage (A), palmella stage after several fissions (B), and flagellate stage 

 (C). D, E. Exuviella perforata Gran, valve view and ventral view; xl230 

 approx. (after Lebour). F, G. Oxyrrhis marina Dujardin, ventral and dorsal 

 views; x875 (after Hall). H. Oxyrrhis teiitaculifera Conrad, ventral view 

 showing long tentacle; xl890 (after C.). I. Gymnodinium catenatum, chain 

 formation; x350 (after Graham). 



