Mallomonas Perty, 1852

Holotype species: Mallomonas ploesslii Perty

Original publication and holotype designation: Perty, M. (1852). Zur Kenntniss kleinster Lebensformen: nach Bau, Funktionen, Systematik, mit Specialverzeichniss der in der Schweiz beobachteten. pp. 1-228, 17 plates. Bern: Verlag von Jent & Reinert.

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Description: Cells solitary, surrounded by an envelope of silica scales. Scales consist of a perforated basal plate, often overlain by secondary patterns. In most species some or all scales bear silica bristles. In the species considered most primitive (section Mallomonopsis, etc.), scales without or only with scant secondary structures. In most species (section Mallomonas and others), scales are tripartite, comprising a dome, shield and flange. Usually a distinct succession of scale types occurs: collar scales (often asymmetric), domed body scales, domeless body scales, and tail scales (often spine bearing). Bristles either glued to the scale (primitive species), or articulated by a special foot in the concavity of the dome (when present). Bristles are tubular with a longitudinal slit, smooth or serrated, the tips may be intricately shaped. Several types of bristles may occur in one cell and may be environmentally determined. In species considered primitive the serration is on the edge, along the slit: craspedodont. Advanced species have teeth not along the edge but as hollow bulges from the opposite side: notacanthic. Both scales and bristles form inside the cell. Vesicles form on the outer side of the chloroplast as bulges from the chloroplast ER. They fuse with Golgi vesicles and are cut off and serve as deposition and molding vesicles for scales and bristles. These begin as flat elements and then roll up into shape. After completion, they are extruded from the cell and arranged in the definite imbricate pattern on the cell surface. Scales and bristles apparently form independently and combine only after extrusion. Cell biflagellate, but in most species, except the subgenus Mallomonopsis, the smooth flagellum is reduced to a short stump not visible by light microscopy. It bears a swelling thought to be a photoreceptor. The hairy flagellum has 2 rows of tripartite hairs and in a few species has been shown to be covered with small annular scales. Flagella have parallel basal bodies and emanate from a flagellar pit. By means of a well-developed rhizoplast they are connected to the outer nuclear membrane. Each cell contains a bilobed chloroplast without stigma. In front of the nucleus a large Golgi, behind a chrysolaminaran vacuole. Asexual reproduction by longitudinal division, during which process the cell covering is reestablished. Sexual reproduction, known in a few species, is isogamous with lateral or caudal fusion. Zygotes develop silicified walls. Germination not observed. Stomatocysts observed in about half the species, spherical or ovoid, and the porus sometimes surrounded by a collar. Surface is smooth or has a species-specific ornamentation. Stomatocyst formation has been followed in M. caudata. The silica wall is deposited endogenously, leaving some protoplasm outside. The porus is formed secondarily and then closed with a plug. The cyst is uni-nucleate, with a large chrysolaminaran vesicle and lipid droplets. Based on scale and bristle ultrastructure the genus has been divided into 17 sections and a total of almost 120 species. Many species described before EM cannot be recognized because theirscale structure is unknown, but in several cases it has been possible to harmonize microscopically described species with EM based taxonomy. Silicified Mallomonas cysts and scales often preserve well in lake sediments. This and recent knowledge of the ecology of Mallomonas spp. have been combined toward reconstruction of lake history, especially as regards eutrophication and acidification. Stomatocysts are better preserved than scales, but only a few can be referred to species. (Nygaard (1956), Sandgren and Carney (1983), Smol and others (1984). Common in plankton of freshwater bodies; a few are brackish. Nearly worldwide distribution.

Information contributed by: J. Kristiansen. The most recent alteration to this page was made on 2021-10-08 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as feminine.

Most recent taxonomic treatment adopted: Kawai, H. & Nakayama, T. (2015). Introduction (Heterokontobionta p.p.), Cryptophyta, Dinophyta, Haptophyta, Heterokontophyta (except Coscinodiscophyceae, Mediophyceae, Fragilariophyceae, Bacillariophyceae, Phaeophyceae, Eustigmatophyceae), Chlorarachniophyta, Euglenophyta. In: Syllabus of plant families. Adolf Engler's Syllabus der Pflanzenfamilien. Ed. 13. Phototrophic eukaryotic Algae. Glaucocystophyta, Cryptophyta, Dinophyta/Dinozoa, Haptophyta, Heterokontophyta/Ochrophyta, Chlorarachnniophyta/Cercozoa, Chlorophyta, Streptophyta p.p. (Frey, W. Eds), pp. 11-64, 103-139. Stuttgart: Borntraeger Science Publishers.

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 08 October 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 22 February 2024

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