Petalomonas | |
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Scientific classification | |
Domain: | |
Phylum: | |
Class: | |
Order: | Petalomonadida
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Family: | Scytomonadidae
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Genus: | Petalomonas F. Stein, 1859
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Petalomonas is a genus of phagotrophic, flagellated euglenoids. [1] Phagotrophic euglenoids are one of the most important forms of flagellates in benthic aquatic systems, playing an important role in microbial food webs. [2] The traits that distinguish this particular genus are highly variable, especially at higher taxa. [2] However, general characteristics such as a rigid cell shape and single emergent flagellum can describe the species among this genus.
Petalomonas was first described by Dr. Friedrich Stein, a zoologist at the University of Prague, in 1859. [3]
Petalomonas is a cosmopolitan genus, most abundant in fresh water with a few species observed in marine environments. [1] [4] These euglenoids mainly reside in muddy sediments as benthic organisms. [5] The cells are phagotrophic, feeding on bacteria, and/or osmotophic, assimilating nutrients from its surroundings. [1] [6]
These non- metabolic, colourless cells range in size from 8–45 um, with a general flattened, leaf-like shape. [1] 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. [1] [4] A distinguishing feature of the euglenoids is the presence of proteinaceous pellicle strips that are underlined with microtubules. [7] 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. [7] 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. [5] Strong ribs or keels are also evident in these cells, which can be arranged spirally or relatively straight, ranging in width. [1] [4] 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. [4] The cells also have an abundance of paramylon bodies, typically used for the storage of starch, that are observed in all species. [1] [4]
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. [8] [5] The cells within this genus are also defined by one emergent flagellum extending from a sub-apical opening, directed anteriorly when swimming. [1] [7] [4] 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. [4] These euglenoids have also been observed to glide forward using the body, while the flagellum is used to contact the substrate. [7] [4] The nucleus is located centrally to the left side of the cell. [4]
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. [6]