The Mastigophora 143 



Suborder 2. Gymnodinina. These are the unarmored dinoflagellates 

 (159) which, except for some of the Gymnodiniidae, are limited to salt 

 water. 



Family 1. ProtoJioctilucidae. The girdle and sulcus are rudimentary 

 and the transverse flagellum is not appreciably flattened. A tentacle is 

 characteristic. There are no chromatophores and the organisms are holo- 

 zoic. The family includes Oxyrrhis Dujardin (Fig. 4. 19, F-H) and Proto- 

 noctiluca Fabre-Domergue (Protodinifer Kofoid and Swezy). In the latter 

 (Fig. 4. 17, E), the shallow girdle extends about one-fourth the circum- 

 ference of the body, and the tentacle, arising from the sulcus, is more 

 pronounced than in Oxyrrhis. Only one pusule is present. The longitu- 

 dinal flagellum is vestigial in Protonoctiliica but is well developed in 

 Oxyrrhis. 



Family 2. Gymnodiniidae. Both girdle and sulcus are well developed 

 and the transverse flagellum is typically flattened. Neither a tentacle nor 

 an ocellus is present. Some species lack chromatophores and a number 

 are holozoic. The family, represented in both fresh and salt water, in- 

 cludes the following genera: Amphidinium Claparede and Lachmann, 

 Cochliodiniuni Schiitt, Gyinnodiniiim Stein em. Kofoid and Swezy, Gyro- 

 diniiim Kofoid and Swezy {Spirodinium Schiitt), Massartia Conrad (10, 

 31, 44), and Torodininm Kofoid and Swezy (159). 



The genera may be distinguished largely on the basis of their girdles. The girdle 

 forms one complete turn in Amphidinium, Gymnndinium, Massartia, and Torodinium. 

 In Amphidinium (Fig. 4. 20, E) the girdle is anterior, so that the epicone is small. The 

 girdle of Gymnodinium (Figs. 4. 17, D, 4. 20, D) lies nearer the equator and the ends 

 are displaced less than one-fifth the body length. Massartia differs from Gymnodinium 

 in having a larger and broader epicone. The girdle of Torodinium (Fig. 4. 20, C) is 

 posterior and the epicone is several times as long as the hypocone. Posteriorly, the 

 sulcus forms a half-turn around the body before intersecting the girdle. In Gyrodinium 

 (Fig. 4. 20, A, B) the girdle makes 1.0 to less than 1.5 turns and the ends are dis- 

 placed not less than one-fifth the body length. The girdle of Cochliodiniuni (Fig. 4. 

 20, F) makes 1.5 or more turns around the body. 



Family 3. Polykrikidae. The single genus, Polykrikos Biitschli (Fig. 4. 

 20, G), contains permanent linear somatellae composed of two, four, or 

 eight zooids as a rule, although chains of sixteen have been observed, 

 Nematocysts are present. All species are marine. 



Family 4. Noctihicidae. The diagnostic feature is a mobile tentacle 

 which arises in the sulcal area and extends posteriorly. The known spe- 

 cies are marine. Two genera, Noctihica Suriray and Pavillardia Kofoid 

 and Swezy, are assigned to the family. Pavillardia (Fig. 4, 20, H) shows a 

 body and girdle of the Gymnodinium-type, but a longitudinal flagellum 

 is absent and a tentacle arises from the posterior end of the sulcus. In 

 Noctihica (Fig. 4. 20, I), the mature organism is a highly vacuolated 

 spheroidal stage ranging from 200 to 2,000[j, in diameter. A short longitu- 

 dinal flagelJum is present. The girdle is vestigial, and the posterior por- 



