Taxonomy and phylogeny of Pyramimonas vacuolata sp. nov. (Pyramimonadales, Chlorophyta)

Pyramimonas vacuolata Suda, Horiguchi & Sym sp. nov. is described from Okinawa-jima Island, Japan. The species has been characterized using light and electron microscopy and its phylogenetic position inferred based on 18S rDNA and rbcL gene sequences relative to other species. Strains of P. vacuolata were isolated from coastal sand samples collected from two localities in Okinawa-jima. The cells are quadriflagellate but remarkably large for the genus, and the posterior half of the cell is vacuolated. The single parietal chloroplast is olive-green and contains two conspicuous pyrenoids lying on the same transverse plane, slightly anterior to the equatorial region of the cell. The pyrenoids are surrounded by numerous starch grains, and thylakoids randomly traverse the pyrenoid matrix. Two monolayered eyespots are present, situated on the same transverse plane as the pyrenoids. The alga possesses three types of body scales and four types of flagellar scales, inclusive of two types of hair scales. This species is readily distinguished from known species of Pyramimonas by its large cell size, the conspicuous posterior vacuole and the presence of two pyrenoids. The most obvious character of this species is its large posterior vacuole, and this prompted the adoption of the specific epithet 'vacuolata'. Analysis of 18S rDNA and rbcL gene sequences of P. vacuolata relative to those of other species of Pyramimonas shows that it falls, with strong support, in a monophyletic clade representing the subgenus Pyramimonas.