Observations on the flagellar apparatus and peripheral endoplasmic reticulum of the coccolithophorid, Pleurochrysis carterae (Prymnesiophyceae)

Abstract

The flagellar apparatus of the motile, coccolith-bearing cells of Pleurochrysis carterae (Braarud & Fagerlund) Christensen is described in detail. The basal part of the flagellar axoneme contains a previously undescribed spiral structure (a helical band) and the transition region consists of a distinctive axosome and at least five tiers of transitional rings. The longer flagellumis shown to be the left (posterior) flagellum of accepted prymnesiophyte nomenclature. The microtubular flagellar roots are similar to those in Pleurochrysis sp. (Inouye & Pienaar 1985); however, we show that the root that consists of a broad sheet of microtubules is associated, at its proximal end, with the forming face of the Golgi body and then becomes partially enveloped by peripheral endoplasmic reticulum (PER) as it extends for the entire length of one side of the cell–this whole structure is termed a cytoplasmic tongue. The PER exhibits a distinctive decoration at specific points on its membrane surface; the importance of this decoration is discussed, along with the ramification of the PER and its possible role in scale/coccolith secretion and the endocytosis of particulate material from the medium. A putative example of endocytosis in P. carterae is presented.