SOME ASPECTS OF TAXONOMY IN THE CRYPTOPHYCEAE

Abstract

The class Cryptophyceae is one of the best defined among Flagellata. Although there is possibly some relation to Dinophyceae, the lines of demarcation are perfectly clear. Furthermore, there seems to be no transition to a true algal state, with the possible exception of Tetragonidium (of. p. I44). Characteristic features of Cryptophyceae are: the peculiar, asymmetrical shape of the cell; the two slightly different flagella, exhibiting a special kind of movement and causing a characteristic type of locomotion, generally recognizable under low power, and involving a change of direction at the slightest irritation; in addition, there is a jerky backward movement caused by stronger harmful influences; the single contractile vacuole near the front end; the inability to form a cell wall; the absence of sexual reproduction; the possession of trichocysts lining a furrow or a gullet; the one or two parietal chromatophores and the deposition of starch as a reserve material. Diversity within the class comprises: absence or presence of a gullet; size and shape of the cell; the kind of accessory pigments, apart from chlorophyll, and their concentration, with the resulting variation in the tint of the chromatophores; possession or lack of pyrenoids; and in rare cases the existence of an eye spot. In a few species chromatophores are lacking. The uniformity of organization renders a subdivision of the class into orders, families and genera difficult, the more so as only few species have been adequately described. The reasons for the lack of solid knowledge are: the scarce occurrence of many Cryptophyceae, which are often found in relatively small numbers amid a rich flagellate population; the complicated shape of the body which is not readily represented by drawings; the abundance of starch which often obscures the internal structure of the cell; the incessant mobility and difficulty of fixing the organisms for closer examination and for staining. Some of these handicaps can be overcome by cultivation, whereby many uniform cells, all originating from one individual, are obtained. Such material can be examined