38 
The sysytematics of ochromonas (chrysophyceae)

Abstract

Ochromonas sensu lato is the largest genus in the Chrysophyceae, containing over 100 names. Ochromonas species are biflagellate, naked, plastid‐bearing single cells, distinguished from loricate, scaled, colonial and colorless genera. Most, if not all, species of Ochromonas are mixotrophic, i.e., they photosynthesize but they also engulf bacteria and other small prey. Preliminary evidence from SSU rRNA sequences show that Ochromonas is a polyphyletic genus. Ochromonas tuberculata is the most distinct from all other Ochromonas species. The other Ochromonas species (examined thus far) are scattered in three clades. For example, O. danica and O. sphaerocystis are sister to Poterioochromonas stipitata and P. malhamensis. Four additional species (identified by light microscopy as O. elegans Doflein, O. globosa Skuja, O. ovalis Dolfein, O. sociabilis Pringheim) have SSU rRNA sequences identical to P. malhamensis. Of these, only O. sociabilis has been transferred to Poterioochromonas. Thus, at least some species may be synonymous with others. Two clades of marine species are also known, one containing coastal species and the other containing open ocean species. A number of genera (some also polyphyletic) are interspersed amongst the Ochromonas species (e.g., Chrysolepidomonas, Chrysonephele, Chrysoxys, Cyclonexis, Dinobryon, Epipyxis, Uroglena, Uroglenopsis). The goal of this research (just beginning) is to establish a monophyletic Ochromonas, probably by assigning some species to other genera (existing or new). One major problem is that the type species, O. triangulata Vysotskii, hasn't been observed in over 100 years, and it is unclear which of several clades of Ochromonas contains the type. Results will be discussed.

Genetic Diversity of Small Eukaryotes in Lakes Differing by Their Trophic Status

“…Cells can also escape from their loricae and are then indistinguishable from Ochromonas spp. (14,17). Paraphysomonas is characterized by siliceous scales on the cell surface, but these scales cannot be easily seen with light microscopy (7).…”

Prey element stoichiometry controls ecological fitness of the flagellate Ochromonas danica

“…Ochromonas is the most species-rich genus in the Chrysophyceae and is distributed throughout freshwaters (Edgar & Andersen 2003). O. danica contains plastids, but will not grow autotrophically at ambient CO 2 levels (Aaronson & Baker 1959).…”