Chapter 12 

 Order 6 Dinoflagellata Biitschli 



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 produce numerous 

 asymmetrical forms. The furrows, or grooves, are a transverse an- 

 nulus and a longitudinal sulcus. The annulus is a girdle around the 

 middle or toward one end of the body. It may be a complete, 

 incomplete or sometimes spiral ring. While the majority 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 envelope is not developed, 

 the terms epicone and hypocone are used (Fig. 105). The sulcus 

 may run from end to end or from one end to the annulus. The two 

 flagella arise typically from the furrows, one being transverse and 

 the other longitudinal. 



The transverse flagellum which is often band-form, encircles the 

 body and undergoes undulating movements, which in former years 

 were looked upon as ciliary movements (hence the name Cilioflagel- 

 lata). In the suborder Prorocentrinea, this flagellum vibrates freely 

 in a circle near the anterior end. The longitudinal flagellum often 

 projects beyond the body and vibrates. Combination of the move- 

 ments of these flagella produces whirling movements characteristic 

 of the organisms. 



The majority of dinoflagellates possess a single somewhat massive 

 nucleus with evenly scattered chromatin, and usually several endo- 

 somes. There are two kinds of vacuoles. One is often surrounded by 

 a ring of smaller vacuoles, while the other is large, contains pink- 

 colored fluid and connected with the exterior by a canal opening into 

 a flagellar pore. The latter is known as the pusule which functions 

 as a digestive organella (Kofoid and Swezy). In many freshwater 

 forms a stigma is present, and in Pouchetiidae there is an ocellus 

 composed of an amyloid lens and a dark pigment-ball. The majority 



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