A supergroup , in evolutionary biology , is a large group of organisms that share one common ancestor and have important defining characteristics. It is an informal, mostly arbitrary rank in biological taxonomy that is often greater than phylum or kingdom , although some supergroups are also treated as phyla .
14-507: 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-photosynthetic, 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
28-406: A simple animal-plant dichotomy was superseded by a recognition of additional kingdoms, taxonomists generally placed amoebae in the kingdom Protista . When scientists began examining the evolutionary relationships among eukaryotes in the 1970s, it became clear that the kingdom Protista was paraphyletic . Rhizaria appear to share a common ancestor with Stramenopiles and Alveolates forming part of
42-764: A supergroup, such as: Picozoa (possibly belongs to Archaeplastida with limited certainty), Malawimonadida (thought to be related to Metamonada ), Ancyromonadida , Breviatea , Apusomonadida , etc. A possible modern topology of the eToL would be the following (supergroups labeled in bold ): TSAR [REDACTED] [REDACTED] [REDACTED] Haptista [REDACTED] Provora Hemimastigophora Cryptista [REDACTED] Archaeplastida [REDACTED] [REDACTED] [REDACTED] Discoba [REDACTED] Metamonada [REDACTED] Ancyromonadida Malawimonadida CRuMs [REDACTED] Amorphea [REDACTED] [REDACTED] [REDACTED] The term 'supergroup'
56-411: The 'supergroup' label more arbitrary. Currently, the addition of many lineages of newly discovered protists (such as Telonemia , Picozoa , Hemimastigophora , Rigifilida ...) and the use of phylogenomic analyses have brought a new, more accurate supergroup model. These are the current supergroups of eukaryotes: Many orphan groups of free-living protozoa remain left behind, unable to be added to
70-481: The 19th century. In his 1861 classification of the Rhizopoda (amoebae), the zoologist William B. Carpenter proposed the order Reticularia , which consisted of Foraminifera and Gromiida on the basis of their very similar thin, reticulose pseudopodia with granules circulating inside. However, the idea that these organisms and others such as Radiolaria were all related to one another emerged rather recently, with
84-587: The Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith in 2002, who also included the centrohelids and Apusozoa . A noteworthy order that belongs to Ascetosporea is the Mikrocytida . These are parasites of oysters . This includes the causative agent of Denman Island Disease, Mikrocytos mackini a small (2−3 μm diameter) amitochondriate protistan. Similarities between various Rhizaria organisms have been noticed since
98-526: The Foraminifera are marine amoebae that are defined by a dynamic network of pseudopodia , and the production of intricate shells. These amoeba have complex sexual life cycles with meiosis and gamete production occurring at separate stages. Supergroup (biology) Since the decade of the 2000s, the eukaryotic tree of life (abbreviated as eToL) has been divided into 5–8 major groupings called 'supergroups'. These groupings were established after
112-543: The SAR super assemblage. Rhizaria has been supported by molecular phylogenetic studies as a monophyletic group. Biosynthesis of 24-isopropyl cholestane precursors in various rhizaria suggests a relevant ecological role already during the Ediacaran . Rhizaria is a monophyletic group composed of two sister phyla: Cercozoa and Retaria . Subsequently, Cercozoa and Retaria are also monophyletic . The following cladogram depicts
126-598: The absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons ( thecae or loricas ), which are in different clades within Rhizaria made out of opal ( SiO 2 ), celestite ( SrSO 4 ), or calcite ( CaCO 3 ). 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
140-971: The evolutionary relationships between all rhizarian classes , and is made after the works of Cavalier-Smith et al. (2018), and Irwin et al. (2019). Imbricatea [REDACTED] Thecofilosea [REDACTED] Sarcomonadea (paraphyletic) [REDACTED] Helkesea Metromonadea [REDACTED] Granofilosea [REDACTED] Chlorarachnea [REDACTED] Phytomyxea [REDACTED] Gromiidea [REDACTED] Lapot gusevi Foraminifera [REDACTED] Polycystinea [REDACTED] Acantharea [REDACTED] Sticholonchea [REDACTED] Stramenopiles [REDACTED] Alveolata [REDACTED] Complete sexual life cycles have been demonstrated for two lineages ( Foraminifera and Gromia ) and direct evidence for karyogamy or meiosis has been observed in five lineages ( Euglyphida , Thecofilosea , Chlorarachniophyta , Plasmodiophorida and Phaeodarea ). In particular,
154-632: The extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean. The three main groups of Rhizaria are: A few other groups may be included in the Cercozoa, but some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea , parasites of plants and animals, respectively, and the peculiar amoeba Gromia . The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of
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#1732772722164168-625: The help of molecular phylogenetics and advanced microscopy techniques in the late 20th century. Rhizaria are part of the SAR supergroup (Stramenopiles, Alveolates, Rhizaria), a grouping that had been presaged in 1993 through a study of mitochondrial morphologies. SAR is currently placed in the Diaphoretickes along with Archaeplastida , Cryptista , Haptista , and several minor clades. Historically, many rhizarians were considered animals because of their motility and heterotrophy . However, when
182-504: The idea that only monophyletic groups should be accepted as ranks, as an alternative to the use of paraphyletic kingdom Protista . In the early days of the eToL six traditional supergroups were considered: Amoebozoa , Opisthokonta , " Excavata ", Archaeplastida , " Chromalveolata " and Rhizaria . Since then, the eToL has been rearranged profoundly, and most of these groups were found as paraphyletic or lacked defining morphological characteristics that unite their members, which makes
196-404: 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
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