Ultrastructure of Draparnaldia glomerata (Chaetophorales, Chlorophyceae). 1. The flagellar apparatus of the zoospore

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Abstract
The fine structure of the quadriflagellate zoospores ofDraparnaldia glomerata(Vauch.) Agardh is described with emphasis on the flagellar root system and compared with the flagellar apparatus of related green algae. It is demonstrated that the flagellar root system inDraparnaldiais similar to that of the zoospore ofUronema belkae.Common features include presence of a cruciate root system (formula 2–5–2–5), prominent striated distal fibre connecting opposite basal bodies, a system I striated root component associated with the 2–stranded root, association of electron dense material with the 5–stranded root, mode of arrangement of the basal bodies in the absolute configuration model, and presence of four striated peripheral fibres interconnecting adjacent basal bodies. Differences exist in the shape of the striated peripheral fibres, the origin of the 2– and 5– stranded roots in the proximal part of the flagellar apparatus, and the architecture and striation pattern of the proximal part of the system I fibre that detaches from the 2–stranded root between adjacent basal bodies. Both the 2– and 5–stranded roots originate near the basal bodies and descend deeply into the zoospore. One of the 5–stranded roots passes near the eyespot of the chloroplast. The implications of these findings for the taxonomic position of the genusDraparnaldiaare discussed. In addition, an evaluation is given of the present status of the order Chaetophorales. Suggestions are given to standardize some aspects of the current terminology of the cruciate flagellar root system in green algae.