Bourrelly : Loricae & Cysts in Chrysophyceae 429 



The genus Uroglena (figure 9) which shows a great structural and cytologic 

 homogeneity, is an excellent example of the diversity form of the cysts, in fact, 

 here knowledge of the cyst is indispensable for the determination of the species. 



The cysts of many unicellular Chrysophyceae are still unknown. On the 

 other hand, many cysts are known in which the free vegetative phase is un- 

 known. This has led the protistologists and the micropaleontologists to give 

 genus and species names to the cysts of which the vegetative phase is unknown. 

 It is a convenient method, but these are not true species, only provisional 

 names without classification value. 



The fresh water cysts, both fossils and recent have been placed in the 

 pseudofamily of the Chrysostoniataceae, whereas the fossil marine cysts make up 

 the Archaemonadaceae. 



The Chrysostomalaceae (figures 8 and 10) are abundant in the present 

 and fossil peat bogs, and in the Diatomae lacustrine deposits. More than 

 200 forms have been observed from the Tertiary period to the present time. 

 The fossil marine forms of the Archaemonadaceae are found in association 

 with Diatomae from the Cretaceous and Tertiary periods (less than 100 fos- 

 sil forms are known). 



The fossihzation of the cysts is often perfect (the pore plug usually being 

 missing, however) whereas that of the loricae of Chrysophyceae seems much 

 more diiBcult, and observations of fossil loricae have been very rare (2 or 3 

 observations only). 



In closing, it must be noted that although the present Chrysophyceae are 

 well known in fresh waters, the forms of marine nanoplankton are very scant 

 because their study has been much neglected. There is a vast domain in which 

 investigation has only begun, and the rare current projects in this field have 

 already yielded a harvest of interesting and novel facts. 



Reference 

 Bourrelly, P. 1957. Bull. Micr. Appl. n. s. 7(5): 118-124. 



