Light and electron microscopical studies on Pseudoscourfieldia marina, a primitive scaly green flagellate (Prasinophyceae) with posterior flagella

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Abstract
The supposedly primitive prasinophyte Pseudoscourfieldia marina has been established in culture and examined in detail. The cells swim by means of two unequal but parallel posterior flagella. Pseudoscourfieldia differs from other green flagellates in the structure of the flagellar root system, possession of a conspicuous leaflike attenuated extension from one basal body into the cell, the structure of the pyrenoid, which is invaginated by long extensions from the mitochondrial complex, and the structure of the scaly covering on the body. Pseudoscourfieldia shows distinct similarities to Nephroselmis, which is laterally biflagellate, and to the Tetraselmis group, which possesses four anterior flagella. The attachment of the hair scales on the flagella has been examined in detail for the first time in a green flagellate. The very short hair scales attach to the flagellar surface between each pair of longitudinal rows of scales known as Melkonian's rows, associated with the inside of every third scale in one row. This is probably a feature common to all prasinophytes with Melkonian's rows. Based on the many investigations now published, a classification for the prasinophytes, supposedly some of the most primitive green algae, is suggested. One class, two orders, and four families are recognized and defined, with 15 genera.