PHYTOFLAGELLATES 113 



by Parke, Manton, and Clarke (1955, 1956), the electron micro- 

 scope was used only to determine the external morphology of 

 the whole body and appendages and the fine structure of the 

 scales. Later (Parke, Manton, and Clarke, 1958, 1959; Manton 

 and Leedale, 1961a, 1961b), thin sections of C. chiton, C. strobilus, 

 C. ericina, C. minor, and C. kappa revealed the internal structure 

 of the haptonema. The wall of this filament consists of three 

 concentric membranes, rather widely separated in the fixed 

 specimens. At least the outer membrane is three-ply. Within the 

 innermost membrane, and often adherent to it, are six (C. Strobilus 

 only), seven (all other species), or rarely eight (some individuals 

 of C. kappa; with this exception the numbers are constant within 

 the species) single tubular fibrils about 20-25 m/x in diameter. 

 Unfortunately, few observations were made on the insertion of 

 the haptonema in the cell; some fibrous structure, lying between 

 the two kinetosomes, is apparent in C. ericina and C. kappa. The 

 delicacy of the organelle and its tendency to rupture or blister 

 during fixation (an especially frustrating problem in marine 

 organisms) made it impossible to determine whether any matrix 

 or other structural components were present in the haptonema, 

 but many evidently intact specimens showed no other constituents. 

 Since the whole filament is capable of tight coiling and rather rigid 

 extension, it constitutes a particularly tantalizing example of a 

 contractile organelle with fairly simple structure. 



Two brief observations on whole mounts of chrysomonads by 

 Pitelka and Dougherty (unpublished) may be mentioned in 

 passing. Monochrysis is classed by Hollande (1952a) as a uniflagel- 

 late, but in electron micrographs M. lutheri (Fig. 38, PL XI) is 

 seen to have one long and one short flagellum, both simple, plus 

 a tiny stub of a third appendage. A similar third stub exists in 

 Vrymnesium parvum, where the two flagella are more nearly equal 

 in length. Prymnesium has been placed with Chrysochromulina in 

 the triflagellate family, Prymnesiidae. Conceivably, the third 

 appendage in these organisms might represent something com- 

 parable to a haptonema; the existence of a third true flagellum in 

 any chrysomonad remains to be demonstrated. 



In the species of Chrysochromulina studied in thin section, the 

 two or four chloroplasts are arranged parietally about the central 

 nucleus, but distortions may occur with changes in body shape. 



