New observations on the CoccolithophoridUmbilicosphaera sibogaevar.foliosa(Prymnesiophyceae) with reference to cell covering, cell structure and flagellar apparatus

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Abstract
Unialgal cultures of the coccolithophorid Umbilicosphaera sibogae (Weber-van Bosse) Gaarder var. foliosa (Kamptner) Okada et McIntyre were investigated using light and electron microscopy. In culture this species is unicellular and non-flagellate, dividing by simple binary fission. The coccosphere is composed of circular placoliths of a single type. Each coccolith consists of four different types of calcified elements deposited on a patternless base-plate scale. Unusual coccoliths similar to those of the type variety U. sibogae (Weber-van Bosse) Gaarder var. sibogae as well as abnormal coccoliths were also observed in culture. Uncalcified body scales are completely absent. There are two to six chloroplasts each containing an immersed pyrenoid, the matrix of which is surrounded by a thin envelope. The nuclear envelope is confluent with the chloroplast endoplasmic reticulum. The endoplasmic reticulum also extends towards the Golgi region and surrounds the Golgi cisternae in which single coccoliths are produced. Flagellate cells were never observed though the flagellar apparatus is persistently present. This consists of two basal bodies linked by proximal and distal bands, eight microtubules of the haptonema base and three asymmetrically arranged microtubular roots. Two of the roots are compound, consisting of two sets of microtubules and the third is simple consisting of at least four microtubules. The taxonomy of U. sibogae var. sibogae and U. sibogae var. foliosa as well as the taxonomic importance of the cell covering is discussed. The flagellar apparatus is compared with that of Pleurochrysis and its importance as a phylogenetic marker is discussed.

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