Zoospore flagellar apparatus architecture and the taxonomic position of Phaeophila dendroides (Ulvophyceae, Chlorophyta)

The quadriflagellate zoospores of Phaeophila dendroides (P. Crouan et H. Crouan) Batters (Chlorophyta), a cosmopolitan marine filamentous ‘chaetophoraceous’ microalga, have ultrastructural features that conform to the pattern characteristic of members of the class Ulvophyceae. The flagellar apparatus exhibits 180° rotational symmetry and a counterclockwise absolute configuration of major components. Unique flagellar apparatus features include six microtubular rootlets, and single-lobed terminal caps. The results suggest that the nearest extant relatives of P. dendroides are filamentous members of the order Ulvales. The structural and reproductive features of P. dendroides cannot be accommodated in any of the existing orders and families of the Ulvophyceae, and therefore the Phaeophilales ord. nov. and Phaeophilaceae fam. nov. are proposed. Phaeophila dendroides probably does not represent a phylogenetic intermediate between the Ulvales and other orders of Ulvophyceae.