The ultrastructure and taxonomy of the Chrysophyceae and Prymnesiophyceae (Haptophyceae): a survey with some new observations on the ultrastructure of the Chrysophyceae

Abstract

Information on the internal structure of the Chrysophyceae is reviewed and some new data are presented. From these a model has been constructed which represents the combination of features constructed to be the basic pattern of cell structure in this group. A brief review is given of modern research, which demonstrates that the choanoflagellates should be removed not only from the Chrysophyccae but also from the plant kingdom. The organization of the Prymnesiophyceae classis nova (= Haptophyceae) is compared with that of the Chrysophyceae, and the relationship of both groups to the Xanthophyccae, Phaeophyceac anti Bacillariophyceae is considered. This leads to the conclusion that the Prymnesiophyceae must be considered as a class separate from the Chrysophyceae. Removal of the Prymnesiophyceae and choanoflagellates from the Chrysophyceae leaves a largely homogeneous and monophyletic group, though the family Pedinellaceae appears to have a unique organization and may be found to be separated from the Chrysophyccae by a phyletic distance at least as great as that between the remaining classes of heterokont algae. It is suggested that this family should occupy a more isolated position in the Chrysophyceae than at present, possibly in a separate order Pedinellales.