Oymnodiniacex 



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Family Gymnodiniacese. 



This group is distinguished by the absence from the motile stages of the 

 life-history of anything of the nature of a strong cellulose wall, such as 

 is possessed by other Peridiniese. Most forms are furnished with a con- 

 tinuous plasma-membrane of great delicacy, and some are enveloped in 

 a wide mucous investment. Sometimes the gelatinous investment is so loose 

 and diffluent that the naked cell is able to move about within it. The 

 vegetative, which is also the motile, state varies in shape from a rounded 

 or egg-shaped cell to an elongate, spindle-shaped body. 



The transverse furrow is a groove or trough in the peripheral plasma. 

 It is ring-like in Gymnodinium (fig. 36 A and B), but in Hemidinium only 

 the left half is developed. In Spirodinium (fig. 36 C and D) it takes the 

 form of an ascending spiral which makes more than a complete turn, and 



Fig. 36. Outline figures of several of the Gymnodiniacese. Only the longitudinal flagellum is 

 shown. A , Gymnodinium carinatum Schilling, x 520 (after Schilling) ; B, G. palustre 

 Schilling, x 750 (after Schilling) ; C, Spirodinium hyalinum (Schilling) Lemm., x 680 (after 

 Schilling) ; D, Sp. spirale (Bergh) Schiitt, x 500 (after Schiitt) ; E and F, Cocklodinium 

 strangulatum Schutt, x 160 (after Schiitt); E, ventral view ; F, dorsal view, i./., longitudinal 

 furrow; tr.f., transverse furrow. 



in Cochlodinium (fig. 36 Z? and F) it makes several spiral turns. In Amphi- 

 dinium the transverse furrow is so near the anterior end of the cell that the 

 apical half appears almost as a lid to the rest of the cell (fig. 37). The 

 longitudinal furrow is much less prominent than the transverse furrow, 

 which it crosses. In Gymnodinium paradoxum Schill. and G. pulvisculus 

 Klebs it is practically absent, and in a number of other forms it is only 

 feebly developed, extending but a little way on either side of the transverse 

 furrow. When the latter is spirally disposed, as in Cochlodinium, the 

 longitudinal furrow has also a spiral twist. In the genus Spirodinium there 

 are often two longitudinal flagella in place of the more normal solitary one. 



The protoplast is colourless, or, as in Cochlodinium archimedes, uniformly 

 tinted; and in Pouch etia there are numerous red droplets in the peripheral 



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