CHAPTER X 



GYMNODINIIDAE : HEMIDINIUM, AlIPHIDINIUM 

 Family 2. GYMNODINIIDAE Kofoicl 



Gymnodinida Bergh {1881&), p. 274. Subfamily. 

 Gymnodinieae, Schiitt (1896), p. 3. 



Amphidinieae Sehonichen and Kalberlah (1900), p. 229. 

 Gymuodinidae Kofoid (1907a), p. 164; (19076), p. 293. 

 Gymnodiniidae, Poche (1913), p. 162. 

 Kyrtodiniaceae Schilling (1913), p. 12. 



Diagnosis. — Gymnodinioidae with girdle varying in length from 0.5 to 4 

 turns around the body; sulcus extending from near apex to near antapex; 

 ocellus and tentacle lacking; pusules usually present; plasma may contain 

 chromatophores, colored pigment or be itself highly colored. Length, 11 to 

 221/^ They are found in both fresh and salt water, are eupelagic, neritic or 

 littoral, and occur in arctic, cool and warm temperate and tropical waters. 



Description. — The members of this family show a progressive differentiation of the body as 

 shown in the length of the girdle and the torsion of the body resulting therefrom. Both sulcus 

 and girdle are well developed, the latter varying in length from 0.5 to 4 turns around the body, 

 with a corresponding lengthening of the sulcus. With the increasing torsion of the body the 

 length of the sulcus increases mainly in the intercingular area, rarely showing apical or antapical 

 loops. The nucleus generally lies near the center of the body and may or may not have a 

 perinuclear membrane. Its chromatin contents are always arranged in characteristic long, monili- 

 form chromatin strands. Pusules are usually present, opening anteriorly into the anterior and 

 posteriorly into the posterior tlagellar pore, or both may be connected by a slender canal, forming 

 a complete channel between the two openings. 



The plasma may be highly colored and frequently contains colored pigment. Chromatophores 

 are found quite generally in the fresh-water forms, more rarely in the marine species, occurring 

 in Amphidinium, Gymnodinium, and Gyrodinium. Nutrition is both holozoic and holophytic, 

 and apparently both phases may be assumed in the same species; individuals occasionally met 

 exhibited both chromatophores and food bodies in the cytoplasm at the same time. 



The cytoplasm may show a differentiation into ectoplasm and endoplasm or the former may 

 consist only of a thin periplast. Longitudinal striae on the surface of the body are frequent. 

 Cyst formation is frequent, either as the result of the ingestion of large food bodies or as division 

 cysts. It is secreted by the body as a closely adherent membrane, which becomes distended by 

 gradually accumulated fluid between itself and the body. 



This family contains 6 genera : Hcmidinium, with 2 species ; Amphidinium, 22 ; Gymnodinium, 

 76; Gyrodinium, 47; Cochlodinium, 29; and Torodinium, 2, giving a total of 178 species. They 

 form one of the most closely intergrading groups in the Dinoflagellata, with clearly established 

 lines of relationship and evolutionary development. 



We add to this family two new genera, Gyrodinium and Torodinium, and 92 new species 

 distributed among the genera as follows: To Amphidinium; 12 new species; to Gymnodinium, 

 36; to Gyrodinium, 21; to Cochlodinium, 21; and to Torodinium, 1. 



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