PHAEOTHAMNIOPHYCEAE CLASSIS NOVA - A NEW LINEAGE OF CHROMOPHYTES BASED UPON PHOTOSYNTHETIC PIGMENTS, RBCL SEQUENCE-ANALYSIS AND ULTRASTRUCTURE

A new algal class, the Phaeothamniophyceae classis nova, is establishe d from genera formerly classified in the Chrysophyceae (e.g., Chrysapi on, Chrysoclonium, Chrysodictyon, Phaeobotrys, Phaeogloea, Phaeoschizo chlamys, Phaeothamnion, Selenophaea, Sphaeridiothrix, Stichogloea, Tet rachrysis, Tetrapion and Tetrasporopsis) as well as one genus previous ly assigned to the Xanthophyceae (Pleurochloridella). HPLC analysis re vealed the presence of fucoxanthin, diadinoxanthin, diatoxanthin, beta -carotene and heteroxanthin, in addition to chlorophylls a and c, in f our genera (Phaeoschizochlamys, Phaeothamnion, Stichogloea, Pleurochlo ridella). The combination of fucoxanthin and heteroxanthin is known on ly for these organisms. The rbcL sequences of the same four genera, al ong with representatives of other chromophyte classes, were analyzed p hylogenetically and provided independent support for recognition of th e Phaeothamniophyceae as a distinct taxon. These data indicate that th e Phaeothamniophyceae are more closely related to the classes Xanthoph yceae and Phaeophyceae than to the Chrysophyceae. Electron microscopy revealed that Phaeoschizochlamys, Phaeothamnion and Stichogloea posses s electron opaque vesicles at the cell periphery, have a cell wall tha t often appears laminate, form new daughter cell walls via eleutherosc hisis, and have plastids with girdle lamellae and a ring-shaped genoph ore. The flagellar apparatus of Phaeothamnion zoospores (described in a previous study) is chosen as representative of the new class. The fl agella are inserted laterally, basal bodies form an angle of ca. 145 d egrees or more, a multi-gyred flagellar transitional helix is present and tripartite flagellar hairs lack lateral filaments. Genera placed i n the Phaeothamniophyceae are assigned to the orders Phaeothamniales a nd Pleurochloridellales, each with a single family.