Ochromonas moestrupii sp nov (Chrysophyceae), a new golden flagellate from Australia

A new marine species of Ochromonas from Port Philip Bay, Victoria, Australia, was described. Cells were metabolic and various shapes included ovoid, lanceolate, oblong, pyriform, spherical and rarely triangular. Normal cell size ranged from 3 to 6 mm wide and 5 to 9 mm long. The long (hairy or immature) flagellum was 1-3 times longer than the cell body. There was a single chloroplast that contained an inconspicuous pyrenoid. There was no eyespot. Cells frequently contained large numbers of oil droplets as well as one or more chrysolaminarin vacuoles. Cysts were not observed. Cells were both free-swimming and attached to a substrate, often by a cytoplasmic stalk. Free-swimming cells frequently had an irregular posterior end formed by a lobose pseudopod. Vegetative cells were mixotrophic and consumed bacteria by capturing them at the base of the short (mature) flagellum. Cell division was observed in various stages but no complete sequence was observed. Early division was recognized when cells were observed with two pairs of flagella. The flagellar pairs separated, the nucleus divided and the cell elongated. The flagellar pairs moved to the ends of the elongated cell, and various cytoplasmic pseudopods were formed, apparently aiding in the separation of the two daughter cells. The chloroplast divided late during cytokinesis, and in some cases the chloroplast failed to divide, causing one daughter cell to be aplastidic. Flagellar hair ultrastructure revealed the typical tripartite structure as well as numerous fine hairs extended from the tubular shaft. The flagella had a distal transitional helix with six gyres, the pyrenoid was slightly penetrated by a chloroplast membrane and the chloroplast was surrounded by membranes continuous with the outer nuclear membrane. The new alga showed some resemblance to the type species, Ochromonas triangulata.