'''' k: 





Chapter 11 

 Order 6 Dinoflagellata Butschli 



THE dinoflagellates make one of the most distinct groups of the 

 Mastigophora, inhabiting mostly marine water, and to a lesser 

 extent fresh water. In the general appearance, the arrangement 

 of the two flagella, the characteristic furrows, and the possession 

 of brown chromatophores, they are closely related to the Crypto- 

 monadina. 



The body is covered by an envelope composed of cellulose 

 which may be a simple smooth piece, or may be composed of two 

 valves or of numerous plates, that are variously sculptured and 

 possess manifold projections. Differences in the position and 

 course of the furrows and in the projections of the envelope pro- 

 duce numerous asymmetrical forms. The furrows, or grooves, are 

 a transverse annulus and a longitudinal sulcus. The annulus is a 

 girdle around the middle or toward one end of the body. It may be 

 a complete or incomplete ring or sometimes spiral. While the ma- 

 jority show a single transverse furrow, a few may possess several. 

 The part of the shell anterior to the annulus is called the epitheca 

 and that posterior to the annulus the hypotheca. In case the en- 

 velope is not developed, the terms epicene and hypocone are used 

 (Fig. 99). The sulcus may run from end to end or from one end 

 to the annulus. The two flagella arise ty]jically from the annulus, 

 one being transverse and the other longitudinal. 



-Anterior flagellar pore x,^ y — "n. Epicene 



, Transverse flagelluni 



Annulus or girdle _ 



-Sulcus 



Hypocone 

 Longitudinal flagellum [ "^Posterior flagellar pore 



Fig. 99. Diagram of a typical naked dinoflagellate (Lebour). 



The transverse flagellum which is often band-form, encircles 

 the body and undergoes undulating movements, which in former 



216 



