KOPOID AND SWEZY: UNARMORED DINOPLAGELLATA 93 



ReI;ATI0xships to the Metazoa. — The unarmorecl Dinoflagellata present 

 two structural differentiations which occur also as distinctive characteristics 

 of the Coeleuterata, namely, nematocysts and tentacles. The nematocysts of 

 the dinofiagellates are so strikingly similar to those of the coelenterates as to 

 suggest the close relationship of the two groups of organisms. The tentacle of 

 the dinofiagellates arises on the l:)order of tlie sulcus or mouth of these Protozoa 

 as these organs do aromid the mouth of the coelenterate. 



There is also in the dinofiagellates a tendency to form a multicellular soma- 

 tella, exemplified in chain-fonnation in Geratiwm, in the corresponding more 

 temporary phase in Noctihica, and in the more permanent and more massive 

 somatellas of the Blastodiniidae. We find in Polijhrikos (originally described 

 as a larval flatworm) a permanent 2- or 4-celled somatella with nematocysts. 

 The sulci of its adjacent cells or zooids form a contimious mouth capable of 

 capturing and engulfing other Protozoa, diatoms, and even the ova of Sagitta. 



The elemental structures and functions thus presented are suggestive, and 

 possibly highly significant of the path along which pelagic dinofiagellates may 

 have given rise to simple pelagic coelenterates in which cell boundaries and 

 cell layers may have played only a secondary and belated part as the size of the 

 organism increased. If we could put together in one organism the nematocysts, 

 the continuous sulci (mouth), and nudticellular (nudtinucleat) somatella of 

 Poli/krikos along with the tentacle of Noctiluca, one for each constitiieut cell 

 along the side of the mouth, we should have an organism whose structure would 

 appear prophetic of the Coelenterata and one whose affinities to that phylum 

 and to the Dinoflagellata would be patent. 



