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Polypodium (animal)
''Polypodium'' is a genus of cnidarians that parasitizes in the eggs of sturgeon and similar fishes (Acipenseridae and Polyodontidae). It is one of few animals that lives inside the cells of other animals. ''Polypodium hydriforme'' is the only species of this monotypic genus. The parent family (Polypodiidae), order (Polypodiidea) and class (Polypodiozoa) are also monotypic. Taxonomy Unusual characteristics have led to much controversy regarding the phylogenetic position of ''Polypodium'' within metazoans. ''Polypodium'' has traditionally been considered a cnidarian because it possesses nematocysts, the stinging structures characteristic of this phylum. Molecular phylogenetic studies using 18S rDNA sequence data temporarily challenged this interpretation, by finding that ''Polypodium'' is a close relative to myxozoans and suggesting that together they share a closer affinity to bilaterians than cnidarians. Due to the variable rates of 18S rDNA sequences, these results were ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
18S RDNA
18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA in eukaryotes. It is a component of the Eukaryotic small ribosomal subunit (40S) and the cytosolic homologue of both the 12S rRNA in mitochondria and the 16S rRNA in plastids and prokaryotes. Similar to the prokaryotic 16S rRNA, the genes of the 18S ribosomal RNA have been widely used for phylogenetic studies and biodiversity screening of eukaryotes. Research history Along with the 28S and 5.8S rRNA in eukaryotes, the 18S rRNA was early identified as integral structural element of ribosomes which were first characterized by their sedimentation properties and named according to measured Svedberg units. Given its ubiquitous presence in eukaryotic life, the evolution of the 18S rRNA was soon proposed as marker for phylogenetic studies to resolve the evolution of eukaryotes. Structure and function The 18S ribosomal RNA is the structural RNA of the small subunit in the eukaryotic cytoplasmic ribosome. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Huso
''Huso'' is a genus of sturgeons from eastern Europe, Asia, and eastern North America. The genus name is derived from ''wikt:huso, hūso'', the Old High German and Medieval Latin word for "sturgeon", which is also ancestral to ''wikt:Hausen, Hausen'', the German name for the Beluga (sturgeon), beluga sturgeon. Taxonomy Until 2025, ''Huso'' was defined as containing two giant-sized species: the Beluga (sturgeon), beluga from western Eurasia, and the Kaluga (fish), kaluga from East Asia. However, this placement was long found to be Polyphyly, polyphyletic, with the kaluga grouping with other East Asian sturgeon species. In contrast, a large number of Eurasian and two North American species were found to form a large clade with ''H. huso''. In addition, the latter clade was found to be more closely related to the morphologically unusual ''Pseudoscaphirhynchus'' than to any other sturgeon clade. In 2025, this taxonomic conundrum was resolved by reclassifying the kaluga and other P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acipenser
''Acipenser'' is a genus of sturgeons, containing three species native to freshwater and estuarine systems of eastern North America and Europe. It is the type genus of the family Acipenseridae and the order Acipenseriformes. Taxonomy Prior to 2025, ''Acipenser'' contained almost all species in the Acipenseridae outside of ''Huso'' and the "shovelnose" sturgeons (''Scaphirhynchus'' and '' Pseudoscaphirhynchus''). However, such a placement is now known to be paraphyletic with respect to the other genera, and these species have since been split into ''Huso'' and '' Sinosturio''. ''Acipenser'' in the strict sense ('' sensu stricto'') has been redefined with only 3 species. This is an ancient genus, with phylogenetic evidence suggesting that it is the most basal sturgeon genus, having diverged from other sturgeons during the Early Cretaceous period. Several fossil species known as far back as the Late Cretaceous, with the fossils of two species ('' A. praeparatorum'' and '' A. a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders of Russia, land borders with fourteen countries. Russia is the List of European countries by population, most populous country in Europe and the List of countries and dependencies by population, ninth-most populous country in the world. It is a Urbanization by sovereign state, highly urbanised country, with sixteen of its urban areas having more than 1 million inhabitants. Moscow, the List of metropolitan areas in Europe, most populous metropolitan area in Europe, is the capital and List of cities and towns in Russia by population, largest city of Russia, while Saint Petersburg is its second-largest city and Society and culture in Saint Petersburg, cultural centre. Human settlement on the territory of modern Russia dates back to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volga
The Volga (, ) is the longest river in Europe and the longest endorheic basin river in the world. Situated in Russia, it flows through Central Russia to Southern Russia and into the Caspian Sea. The Volga has a length of , and a catchment area of .«Река Волга» , Russian State Water Registry It is also Europe's largest river in terms of average discharge at delta – between and – and of . It is widely regarded as the national river of |
Sterlet
The sterlet (''Huso ruthenus'') is a relatively small species of sturgeon from Eurasia native to large rivers that flow into the Black Sea, Azov Sea, and Caspian Sea, as well as rivers in Siberia as far east as Yenisei River, Yenisei. Populations migrating between fresh and salt water (anadromous) have been Local extinction, extirpated. It is also known as the sterlet sturgeon. Due to overfishing (for its flesh, caviar, and isinglass), pollution, and dams, the sterlet has declined throughout its native range and is considered Vulnerable species, vulnerable by the IUCN. Restocking projects are ongoing, and it has been Introduced species, introduced to some regions outside its native range, but the latter have generally not become self-sustaining. Today, the majority of the international trade involves sterlets from aquaculture. Taxonomy Prior to 2025, it was placed in the genus ''Acipenser'', but this placement was found to be Paraphyly, paraphyletic, and it is more accurately ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polypodium Hydriforme A
''Polypodium'' is a genus of ferns in the family Polypodiaceae, subfamily Polypodioideae, according to the Pteridophyte Phylogeny Group classification of 2016 (PPG I). The genus is widely distributed throughout the world, with the highest species diversity in the tropics. The name is derived from Ancient Greek ''poly'' ("many") + ''podion'' ("little foot"), on account of the foot-like appearance of the rhizome and its branches. They are commonly called polypodies or rockcap ferns, but for many species unique vernacular names exist. They are terrestrial plant, terrestrial or epiphyte, epiphytic ferns, with a creeping, densely hairy or scaly rhizome bearing fronds at intervals along its length. The species differ in size and general appearance and in the character of the fronds, which are evergreen, persisting for 1–2 years, pinnate or pinnatifid (rarely simple entire), and from 10 to 80 cm or more long. The sorus, sori or groups of spore-cases (sporangia) are borne on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myxozoan
Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. Over 2,180 species have been described and some estimates have suggested at least 30,000 undiscovered species. Many have a two-host lifecycle, involving a fish and an annelid worm or a bryozoan. The average size of a myxosporean spore usually ranges from 10 μm to 20 μm, whereas that of a malacosporean (a subclade of the Myxozoa) spore can be up to 2 mm. Myxozoans can live in both freshwater and marine habitats. Myxozoans are highly derived cnidarians that have undergone dramatic evolution from a free swimming, self-sufficient jellyfish-like creature into their current form of obligate parasites composed of very few cells. As myxozoans evolved into microscopic parasites, they lost many genes responsible for multice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taxon
In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is very common, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion, especially in the context of rank-based (" Linnaean") nomenclature (much less so under phylogenetic nomenclature). If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping. Initial attempts at classifying and ordering organisms (plants and animals) were presumably set forth in prehistoric times by hunter-gatherers, as suggested by the fairly sophisticated folk taxonomies. Much later, Aristotle, and later st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Science (journal)
''Science'' is the peer review, peer-reviewed academic journal of the American Association for the Advancement of Science (AAAS) and one of the world's top academic journals. It was first published in 1880, is currently circulated weekly and has a subscriber base of around 130,000. Because institutional subscriptions and online access serve a larger audience, its estimated readership is over 400,000 people. ''Science'' is based in Washington, D.C., United States, with a second office in Cambridge, UK. Contents The major focus of the journal is publishing important original scientific research and research reviews, but ''Science'' also publishes science-related news, opinions on science policy and other matters of interest to scientists and others who are concerned with the wide implications of science and technology. Unlike most scientific journals, which focus on a specific field, ''Science'' and its rival ''Nature (journal), Nature'' cover the full range of List of academ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long Branch Attraction
In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lineage is sufficient to cause that lineage to appear similar (thus closely related) to another long-branched lineage, solely because they have both undergone a large amount of change, rather than because they are related by descent. Such bias is more common when the overall divergence of some taxa results in long branches within a phylogeny. Long branches are often attracted to the base of a phylogenetic tree, because the lineage included to represent an outgroup is often also long-branched. The frequency of true LBA is unclear and often debated, and some authors view it as untestable and therefore irrelevant to empirical phylogenetic inference. Although often viewed as a failing of parsimony-based methodology, LBA could in principle result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
