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The cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella. Some may exhibit mixotrophy. They are classified as clade Cryptomonada, which is divided into two classes: heterotrophic Goniomonadea and phototrophic Cryptophyceae. The two groups are united under three shared morphological characteristics: presence of a periplast, ejectisomes with secondary scroll, and mitochondrial cristae with flat tubules. Genetic studies as early as 1994 also supported the hypothesis that Goniomonas was sister to Cryptophyceae. A study in 2018 found strong evidence that the common ancestor of Cryptomonada was an autotrophic protist.
The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally they have the form of small amoebae, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net. They may also form flagellate zoospores, which characteristically have a single subapical flagellum that spirals backwards around the cell body, and walled coccoid cells.
Labyrinthulomycetes (ICBN) or Labyrinthulea (ICZN) is a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrinthulids and thraustochytrids. They are mostly marine, commonly found as parasites on algae and seagrasses or as decomposers on dead plant material. They also include some parasites of marine invertebrates and mixotrophic species that live in a symbiotic relationship with zoochlorella.
The cryptophyceae are a class of algae, most of which have plastids. About 230 species are known, and they are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella.
Thaumatomonadida is an order of flagellates.
Rhodomonas is a genus of cryptomonads. It is characterized by its red colour, the square-shaped plates of its inner periplast, its short furrow ending in a gullet, and a distinctly shaped chloroplast closely associated with its nucleomorph. Historically, Rhodomonas was characterized by its red chloroplast alone, but this no longer occurs as its taxonomy has become increasingly based on molecular and cellular data. Currently, there is some debate about the taxonomic validity of Rhodomonas as a genus and further research is needed to verify its taxonomic status. Rhodomonas is typically found in marine environments, although freshwater reports exist. It is commonly used as a live feed for various aquaculture species.
Goniomonas is a genus of Cryptomonads and contains five species. It is a genus of single-celled eukaryotes, including both freshwater and marine species. It lacks plastids, which is very unusual among all of the Cryptophyte genera. It may reflect one of only a small number of times that the Cryptophytes evolved into freshwater habitats. Goniomonas seems to have a number of freshwater relatives which have not yet been cultured and named.
The apusomonads are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts, the clade that includes both animals and fungi. Together with the Breviatea, these form the Obazoa clade.
Ancyromonadida or Planomonadida is a small group of biflagellated protists found in the soil and in aquatic habitats, where they feed on bacteria. Includes freshwater or marine organisms, benthic, dorsoventrally compressed and with two unequal flagellae, each emerging from a separate pocket. The apical anterior flagellum can be very thin or end in the cell membrane, while the posterior flagellum is long and is inserted ventrally or laterally. The cell membrane is supported by a thin single-layered theca and the mitochondrial crests are discoidal/flat.
The kathablepharids are a group of heterotrophic flagellates (Protists) the first species of which was described by Skuja in 1939 as Kathablepharis phoenikoston. His spelling was challenged because of non-compliance with botanical nomenclatural conditions, hence the alternative spelling Katablepharis. As the organism was heterotrophic and usually regarded as 'protozoan', and to favour stability, Skuja's original spelling has largely prevailed. With an anterior pocket and ejectisomes, the kathablepharids were thought initially to be cryptomonads. There were a variety of differences with Cryptomonas and other typical cryptomonads = cryptophytes, such as the thickness, length, and beat pattern of the flagella, their phagotrophic habitat, differences in the ejectisomes, and various features of their ultrastructure. The distinctive characteristics of the group were established from electron microscopical studies by Clay and Kugrens and Vørs. More recently they have been tentatively grouped with the chromalveolates, or distantly with the cryptophytes.
Collodictyonidae is a group of aquatic, unicellular eukaryotic organisms with two to four terminal flagella. They feed by phagocytosis, ingesting other unicellular organisms like algae and bacteria. The most remarkable fact of this clade is its uncertain position in the tree of life.
Rigifilida is a clade of non-ciliate phagotrophic eukaryotes. It consists of two genera: Micronuclearia and Rigifila.
Varisulca was a proposed basal Podiate taxon. It encompassed several lineages of heterotrophic protists, most notably the ancyromonads (planomonads), collodictyonids (diphylleids), rigifilids and mantamonadids. Recent evidence suggests that the latter three are closely related to each other, forming a clade called CRuMs, but that this is unlikely to be specifically related to ancyromonads
Platysulcus tardus is an eukaryotic microorganism that was recently discovered to be the earliest diverging lineage of the Heterokont phylogenetic tree. It is the only member of the family Platysulcidae, order Platysulcida and class Platysulcea.
Placidozoa is a recently defined non-photosynthetic lineage of Stramenopiles.
Granofilosea is a class of cercozoan protists in the subphylum Reticulofilosa. Out of the three groups that were traditionally considered heliozoans: the heliomonads, gymnosphaerids and desmothoracids, the latter were recently grouped into this new class.
Mantamonads are a group of free-living heterotrophic flagellates that move primarily by gliding on surfaces. They are classified as one genus Mantamonas in the monotypic family Mantamonadidae, order Mantamonadida and class Glissodiscea. Previously, they were classified in Apusozoa as sister of the Apusmonadida on the basis of rRNA analyses. However, mantamonads are currently placed in CRuMs on the basis of phylogenomic analyses that identify their closest relatives as the Diphylleida and Rigifilida.
Hemiarma marina is a monotypic species of cryptomonad discovered off the coast of Palau in 2016.
Tetragonidiaceae is a family of cryptomonads which includes two genera. Members of Tetragonidiaceae are distinguished from other cryptomonads by reproduction occurring in a non-motile vegetative phase, as well as the formation of multicellular filaments unlike any other cryptomonad family.
Pyrenomonadaceae is a family of cryptomonads which includes three or four known genera. They are distinguished from other cryptomonads by their nucleomorphs being imbedded into the pyrenoid, and the presence of distinctive pigment phycoerythrin 545.
References
- ↑ Shiratori; Ishida (2016), "A New Heterotrophic Cryptomonad: Hemiarma marina n. g., n. sp.", Journal of Eukaryotic Microbiology, 63 (6): 804–812, doi:10.1111/jeu.12327, PMID 27218475
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