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Nucleariida is a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid cristae, in the absence of superficial granules, and in the way they consume food.
The Stramenopiles, also called Heterokonts, are a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have been secondarily lost. Stramenopiles represent one of the three major clades in the SAR supergroup, along with Alveolata and Rhizaria.
The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth.
Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections from the amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines. They may be found in both freshwater and marine environments.
Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.
The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons, which are in different clades within Rhizaria made out of opal, celestite, or calcite. Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.
Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.
The tectofilosids are a group of filose amoebae with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales. The shell usually has a single opening, but in Amphitrema and a few other genera it has two on opposite ends. The cell itself occupies most of the shell. They are most often found on marsh plants such as Sphagnum.
Monadofilosa is a grouping of Cercozoa. These organisms are single-celled amoeboid protists.
Imbricatea is a class of Rhizaria characterised by silica scales. It is sometimes described as "Imbricatea/Silicofilosea", due to the similarity of those two groupings. Imbricatea is divided into the orders Euglyphida and Thaumatomonadida.
Thecofilosea is a class of unicellular testate amoebae belonging to the phylum Cercozoa. They are amoeboflagellates, organisms with flagella and pseudopodia, distinguished from other cercozoa by their scale-lacking test composed of organic material. They are closely related to the Imbricatea, a group of testate amoebae with tests composed of inorganic silica scales.
The sarcomonads or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or external theca, a soft cell surface without obvious cortical filamentous or membranous skeleton, two cilia without scales or hairs, tubular mitochondrial cristae, near-spherical extrusomes, and a microbody attached to the nucleus.
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
Rabdiophrys is a genus of amoeboid rhizarians. It has 19 species, including the species Rabdiophrys anulifera.
Raphidiophryidae is a family of mostly freshwater centrohelids. It is the sister family of Acanthocystidae, sharing the trait of presenting silica scales and comprising the clade Chalarothoracina. Two genera, Raphidiophrys and Polyplacocystis, have been discovered so far.
Endohelea is a proposed clade of eukaryotes that are related to Archaeplastida and the SAR supergroup. They used to be considered heliozoans, but phylogenetically they belong to a group of microorganisms known as Cryptista.
Phaeocystida, also known as Phaeocystina, is a group of cercozoans in the class Phaeodarea. It was first described by Ernst Haeckel in 1887 and treated traditionally as a suborder, but later was raised to order level until Cavalier-Smith's classification lowered it again to suborder level. It belongs to the order Eodarida, characterised by simpler silica skeletons or a lack thereof.
Corbihelia is a proposed phylum of eukaryotes.
The paracercomonads are a group of cercozoan protists. Taxonomically, they comprise the family Paracercomonadidae, order Paracercomonadida and subclass Paracercomonada. Due to their morphological similarities to the cercomonads, members of this family were grouped with Cercomonas and similar taxa from the beginning. However, their similarities are due to convergent evolution.
Tetrahelia is a genus of four-ciliated protists belonging to the Endohelea, a group of heterotrophic eukaryotes previously considered heliozoa. It is the only genus in the family Tetraheliidae and order Axomonadida. It is a monotypic genus, containing the sole species Tetrahelia pterbica, previously classified as Tetradimorpha.
References
- ↑ Yabuki A, Chao EE, Ishida KI, Cavalier-Smith T (2012). "Microheliella maris (Microhelida ord. n.), an Ultrastructurally Highly Distinctive New Axopodial Protist Species and Genus, and the Unity of Phylum Heliozoa". Protist. 163 (3): 356–388. doi:10.1016/j.protis.2011.10.001. ISSN 1434-4610. PMID 22153838.
- ↑ Croome, R. L.; van den Hoff, J.; Burton, H. R. (1987). "Observations of the heliozoean genera Pinaciophora and Acanthocystis (Heiliozoea, Sarcodina, Protozoa) from Ellis Fjord, Antarctica". Polar Biology. 8: 23–28. doi:10.1007/BF00297160.
- ↑ Cavalier-Smith, Thomas; Chao, Ema E. (2012). "Oxnerella micra sp. n. (Oxnerellidae fam. n.), a Tiny Naked Centrohelid, and the Diversity and Evolution of Heliozoa". Protist. 163 (4): 574–601. doi:10.1016/j.protis.2011.12.005. PMID 22317961.
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