116 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



whole cells of Gyrodinium sp. (Pitelka and Schooley, 1955). As is 

 characteristic of dinoflagellates, this species has a long, ribbon- 

 shaped transverse flagellum (typically held in a groove encircling 

 the body) and a shorter, slender one directed posteriorly. The 

 breadth of the transverse flagellum is explained by the presence 

 of a unilaterally expanded sheath of low density. In some speci- 

 mens a sparse array of long, flexuous mastigonemes was present, 

 usually on one side only of the flagellum. The posterior flagellum 

 was smooth and tapered to a short acroneme tip. 



Observations on the nuclei of sectioned dinoflagellates (Grell 

 and Wohlfarth-Bottermann, 1957; Grasse and Dragesco, 1957), 

 with their enormous, helically wound interphase chromosomes, 

 have been described in Chapter 2. The paper by Grell and 

 Wohlfarth-Bottermann contains in addition a short account of 

 other protoplasmic structures of A.mphidinium elegans. The many 

 small plastids are oriented approximately radially about the cell 

 periphery and with the abundant starch grains fill up most of the 

 extra-nuclear space. Lamellae run in orderly bands of usually three 

 discs parallel to the long axis of the plastid. The cytoplasm 

 contains many vesicular and tubular profiles and fine granules, 

 microtubular mitochondria, and Golgi structures (noted but not 

 illustrated). The pellicle consists of inner and outer membranes, 

 both described as multilayered, separated by a rather wide clear 

 zone that is traversed by irregular slender strands or tubules. 

 Above the outer membrane is a fringe of projecting fine filaments, 

 believed by the authors to represent the mucoid secretion of 

 mucigenic bodies beneath the surface. 



Like the scales of chrysomonads, the detached thecal plates of 

 dinoflagellates have been examined intact in the electron micro- 

 scope. Fott and Ludvik (1956b) found the plates of Ceratium 

 hirundinella to be rather thick and homogeneous in texture, with 

 evenly arranged depressions leading to circular pores. 



Oxyrrhis marina is a small flagellate of uncertain position, classed 

 as a dinoflagellate in the Grasse treatise (Chatton, 1952) but as a 

 cryptomonad by some other authors. Dragesco (1952b) found no 

 evidence of mastigonemes on its two flagella. Discharged 

 trichocysts resembled those of some ciliates (p. 55). 



Dragesco's observations (1951) on the trichocysts of the 

 cryptomonad, Chilomonas Paramecium, are cited on p. 55. The 



