The flagellar apparatus in the marine flagellate algal genus Oltmannsiellopsis (Dunaliellales, Chlorophyceae)

Summary The actual spatial configuration of the flagellar apparatus of quadriflagellate cells of Oltmannsiellopsis viridis (Dunaliellales Ettl 1983) has been reconstructed in detail by serial sectioning analysis using transmission electron microscopy. For comparison, this apparatus has (in less detail) also been studied in 0. unicellularis . Despite differences in the shape of the emergence site of flagella (no flagellar depression in 0. viridis versus the presence of a shallow flagellar pit in 0. unicellularis ) the flagellar apparatus appears to be quite similar in both species. It shows 180° rotational symmetry. It has a unique architecture, of which the most salient features are: (1) the four basal bodies are arranged in two pairs; (2) the basal bodies forming one pair are arranged almost parallel; (3) the basal body pairs are displaced with respect to each other in the counterclockwise direction and they cross each other proximally at ± 60° (4) the typical proximal orientation of two types of cruciately-arranged microtubular flagellar roots: left root (s root or R4, usually disposed in 3+1 configuration) and right root (d root or R2); (5) the association of each microtubular flagellar root with a very prominent, complex, striated system I fibre; (6) the distal interconnection of the two inner (parental) basal bodies by a remarkable, coarsely striated fibre; (7) the interconnection of the inner basal body of each pair with the outer (progeny) basal body of the complementary pair by at least two accessory striated fibres; (8) the conspicuous proximal striated fibre linking the proximal ends of basal bodies forming a pair, and (9) the attachment of two striated sheath-like appendages to the proximal surface of each basal body pair. In the light of these findings the phylogenetic and taxonomic status of the genus Oltmannsiellopsis is discussed.