ULTRASTRUCTURE OF THE BIFLAGELLATE MOTILE CELLS OF ULVARIA OXYSPERMA (KÜTZ.) BLIDING AND PHYLOGENETIC RELATIONSHIPS AMONG ULVAPHYCEAN ALGAE

The detailed fine structure of the biflagellate motile cells of Ulvaria oxysperma (Kiitz.) Bliding is described. These cells demonstrate most of the features presently used to characterize the ulvaphycean motile cell, i.e., the capping plate, terminal cap, alternating two- and four-membered rootlets, rhizoplasts that extend posteriorly into the cell, the striated microtubule-associated component (SMAC) near the two-membered rootlets, microtubule septations in the basal bodies and flagella, and scales covering the external surface of the cell. In addition, the anterior end components have 180° rotational symmetry. The rootlets insert into the basal body complex in the anterior region just beneath the capping plate, and the rhizoplasts insert into triangularshaped proximal fibers that connect the basal bodies. The features of many other ulvaphycean algae are summarized and compared with Ulvaria oxysperma. Based on comparative ultrastructure, it is suggested that the Ulvaphyceae diverged from the Chlorophyceae after the separation of these two classes from the Charophyceae.