Phylogenetic position of a rare loricated green alga, Cephalomonas granulata N. L. Higinb. (Volvocales, Chlorophyceae)

Cephalomonas ( Cp .) granulata N. L. Higinb. (Volvocales, Chlorophyceae), a rare volvocalean phytoflagellate, has recently been isolated from a paddy field in Japan and examined by light and fluorescence microscopy. The vegetative cells of Cp . granulata have granulate loricae and a characteristic mushroom-like shape with a hemispherical to spherical anterior part and narrower posterior part. Cp . granulata has been classified among the Phacotaceae along with other loricated genera. However, its phylogenetic position has not been investigated using molecular phylogeny. To evaluate the phylogenetic position of Cephalomonas , the 18S r RNA gene sequence of the Japanese strain was determined. The phylogenetic analyses revealed that Cp . granulata was not closely related to other loricated taxa with known phylogenetic affinities, such as Phacotaceae sensu stricto ( Phacotus , Pteromonas , and Wislouchiella ) and Dysmorphococcus globosus . This indicates at least three independent origins of loricae within the Volvocales.