Petalomonas
Petalomonas is a genus of phagotrophic, flagellated euglenoids. Phagotrophic euglenoids are one of the most important forms of flagellates in benthic aquatic systems, playing an important role in microbial food webs. The traits that distinguish this particular genus are highly variable, especially at higher taxa. However, general characteristics such as a rigid cell shape and single emergent flagellum can describe the species among this genus. History of knowledge. "Petalomonas" was first describe by Dr. Friedrich Stein, a zoologist at the University of Prague, in 1859. Habitat and ecology. "Petalomonas" is a cosmopolitan genus, most abundant in fresh water with  a few species observed in marine environments. These euglenoids mainly reside in muddy sediments as benthic organisms. The cells are phagotrophic, feeding on bacteria, and/or osmotophic, assimilating nutrients from its surroundings. Description. These non-metabolic, colourless cells range in size from 8–45 um, with a general flattened, leaf-like shape. The posterior end is rounded or truncate and the anterior end is narrowed; however, cells can span from ovoid, to fusiform or triangular, to elongately oval. A distinguishing feature of the euglenoids is the presence of proteinaceous pellicle strips that are underlined with microtubules. In "Petalomonas", cells are covered with  approximately a dozen thickly, fused pellicle strips making the cell very rigid and possibly resistant to surface ice crystal formation that can disrupt the cell. These pellicle strips, unlike most euglenoids, are lacking grooves or troughs; however, species specific pellicle features, such as pleat-like thickenings at the joints of pellicle strips, that characterize "P. cantuscygni", can distinguish certain species. Strong ribs or keels are also evident in these cells, which can be arranged spirally or relatively straight, ranging in width. Some species may contain furrows that vary in size and depth, and can be located dorsally and/or ventrally on  the body of the cell. The cells also have an abundance of paramylon bodies, typically used for the storage of starch, that are observed in all species. The feeding structure, not visible under light microscopy, is relatively simple consisting of a pocket-like cavity ending with a cytostome, lined with microtubules for phagocytosis. The cells within this genus are also defined by one emergent flagellum extending from a sub-apical opening, directed anteriorly when swimming. The movement of this flagellum is very minimal with some vibration at the tip; however, some species are observed to have vigorously, whipping flagellum that  result in rapid rotation and oscillation of the cell body. These euglenoids have also been observed to glide forward using the body, while the flagellum is used to contact the substrate. The nucleus is located centrally to the left side of the cell. Life history. In euglenoids, sexual reproduction is unknown; however, asexual reproduction has been observed to occur in this genus through longitudinal fission, where the division occurs very quickly, starting at the anterior end of the cell.