LORICAE AND CYSTS IN THE CHRYSOPHYCEAE 



Pierre Bourrelly 

 Museum National d'Hisioire Natiirelle, Paris, France 



The unicellular algae, solitary or colonial, often have their cytoplasm enclosed 

 within shells of various shapes and kinds called loricae or thecae. These 

 thecae are found in numerous phyla of algae: Euglenales (Trachelomonas, 

 Strombomonas), Volvocales (Phacotus, Coccomonas), Dinophyceae (Peri- 

 dinium, Dinophysis, Exuviella), and in numerous Chrysophyceae and Craspedo- 

 monadinae.* 



The Chrysophyceae may have, in addition, a phase of dormancy or of resist- 

 ance in the form of siliceous cysts or statospores. These cysts always have an 

 endogenous origin, and may arise from a simple encystment of a vegetative 

 cell, or, on the contrary, of a zygote resulting from a autogamy or from an 

 isogamic fusion. 



The cysts of the Chrysophyceae are exclusively siliceous, and are of highly 

 varied forms, but they exhibit a pore closed by a silicopectic plug. The forma- 

 tion of a siliceous cyst with a pore and plug is the basic characteristic which 

 enables us to identify the whole Chrysophyceae group without any possibihty 

 of error. 



Certain loricae of the Chrysophyceae {Chrysococcus, for example), are si- 

 liceous, and have very small pore openings. In the absence of a flagellum and 

 the plug which closes the pore, one might easily confuse the cyst and the lorica. 

 In fact, in the Chrysophyceae, the thecae are pierced with a pore opening from 

 which the flagellum (or the flagella) or the pseudopodia emerge. 



Loricae 



If we take as an example of loricated Chrysophyceae, the genus Dinobryou 

 (figure 8) and the kindred genus Hyalobryon, we note that the morphology 

 and the structure of the loricae vary with the species. In the two genera cited, 

 the shell is in the form of a conical or cylindroconical horn, more or less flared out 

 at the apex opening; the cellular body is bound to the lorica by a retractile cysto- 

 plasmic filament, the epipode. The shell is hyaline, of a cellulose-pectic nature, 

 with a marked dominance of the cellulose. The outline of this lorica is either 

 straight or undulating, according to the species The action of coloring agents 

 (Congo Red) causes the appearance of a very fine heHcoidal striation of the 

 wall, accompanied at times by a spiral torsion indicated already by the undulat- 

 ing edge of the theca {Dinobryon divergens (figure 1)). In all of the colonial 

 Dinobryon which were studied, the basic helicoidal striation has the same direc- 

 tion of rotation (counter-clockwise), whereas the marginal undulations display 

 a coiling in the opposite direction. 



Dinobryon suecicum (figure 1), a solitary species, free, with a smooth cellu- 

 lose-pectic lorica, hyaline, with an helicoidal, projecting execresence, brown in 

 color and of an unknown nature (calcareous substance impregnated with iron 

 salt?) running throughout the greater part of its length. 



An analogous feature is found in some Pseudokephyrion. The solitary fixed 



* We will leave out the Silicoflagellates and the family of the Coccolithophoraceae, as 

 these might constitute the subject of a special stud>-. 



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