The cytology and classification of Schizomeris leibleinii (Chlorophyceae). II. The structure of quadriflagellate zoospores

In the first paper of this series it was shown that mitosis and cytokinesis in Schizomeris are more like those events in Stigeoclonium rather than Ulva. It was concluded that Schizomeris should be included in the Chaetophorales. The present work shows that the zoospores of Schizomeris are somewhat different from those of both Stigeoclonium and Ulva. It is concluded that Schizomeris should be retained in a separate family of the Chaetophorales. Specifically, quadriflagellate zoospores of Schizomeris lack a two-stranded microtubular root, but rather have four, wide, cruciately arranged microtubular roots which probably contain an equal number of microtubules. Evolution in green algal motile cells is briefly discussed, and it is suggested that a flagellar ring such as occurs in the Oedogoniales may have evolved from quadriflagellate zoospores similar to those of Schizomeris.