The ultrastructure of the flagellar apparatus of the zoospore of Chaetomorpha melagonium (Web. & Mohr) Kützing (Chlorophyta)

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Abstract
The ultrastructure of the flagellar apparatus of the biflagellate zoospore of Chaetomorpha melagonium (Web and Mohr) Kutzing has been examined by analysis of serial sections. The structure is quite similar to the basic type of flagellar apparatus described for other motile reproductive cells in the phyletic group of Ulvophyceae. Common features include 180.degree. rotational symmetry, counter-clockwise absolute orientation of the major flagellar apparatus components and the presence of terminal caps, four cruciately-arranged microtubular roots, striated syste I fibers (SMAC) and system II fibers. Specific characteristics are found in the composition of the root formula (3-2-3-2), the arrangement of the three-stranded root in a two-over-one configuration, the typical striation pattern of the distal connecting fibre, and the presence of a peculiar trilobed proximal sheath coating the lower half of the basal bodies. The system I fiber associated with the two-stranded root shows a periodicity of c. 16 nm. On the contrary, the system II fiber associated with the three-stranded root does not exhibit a striated pattern hence showing its rudimentary nature. In the light of these findings, the taxonomic position and the status of the Cladophorales and the Ulvophyceae are evaluated.