CHAPTER I 



GENERAL MORPHOLOGY: SIZE AND FORM, MOTOR ORGANELLES, 

 FURROWS AND TORSION OF THE BODY 



The Gymnodinioidae are among the least known of all the dinoflagellates 

 for several reasons. They are in the main fomid in oceanic waters or at least 

 where neritic influences are not potent. This pelagic halntat affords the second 

 reason for the oliscurity surrounding the group, to wit, the very great delicacy 

 of the organisms and their extreme sensitiveness to adverse conditions. At 

 the best it is highly improl)al)le that all the forms belonging to the group sui'- 

 vive the turmoil of the ]3lankton net, the changes in salinity, temperature, 

 pressure, illumination, ionization and proportions of dissolved gases incident 

 upon the transfer from the open sea to the film of water beneath the cover 

 glass, and to the concentrated light of the high-power microscope. For many 

 of them dissolution ensues within a few moments after they are placed under 

 the microscope for observation, with explosive abruptness and utter disruption 

 of all structural features, while even hardier forms contract more or less, 

 undergo profound color changes and lose their characteristic features very soon 

 after exposure to the axial rays of the microscope. 



One of the results of the great susceptibility of these organisms to slight 

 environmental changes has been the frequent appearance in the literature 

 dealing with these forms of figures of abnormal character, caused by changes 

 incident to microscopical examination. Another point which must be consid- 

 ered not only in studying the organisms themselves, but in any review of the 

 literature dealing with them, is the great transparency of their bodies and the' 

 trap which may thus be set for even experienced biologists. The importance 

 of this fact lies in the liability of the operator to mistake the opposite side of 

 the organism under the microscope for the side nearest him or uppermost, witli 

 the result that the orientation of the organism is completely reversed. There 

 are many instances of such reversed orientation recorded in the literature 

 (Kofoid and Swezy, 1917) even among veteran investigators, as that of Nema- 

 todinium armatum, {j^Pouchetia annata) by Dogiel (1906), where the girdle is 

 di'awn as though extending from the ventral face to tlie I'ight of the body and 

 OA'er dorsally to the left, a complete reversal of its actual course. 



These conditions call for caution in dealing with the group, even where an 

 abundance of material and a variety of forms have been present, as in our own 

 work on these organisms. Some of the pitfalls have been avoided, but others 

 xuiwittingly may have been overlooked. 



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