64-452: The Ocypodoidea , or ocypoid crabs, are a superfamily of crabs , named after the genus Ocypode . It contains the following families: This Brachyura article is a stub . You can help Misplaced Pages by expanding it . Taxonomic rank In biology , taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms)
128-499: A BioCode that would regulate all taxon names, but this attempt has so far failed because of firmly entrenched traditions in each community. Consider a particular species, the red fox , Vulpes vulpes : in the context of the Zoological Code , the specific epithet vulpes (small v ) identifies a particular species in the genus Vulpes (capital V ) which comprises all the "true" foxes. Their close relatives are all in
192-402: A cartilaginous / bony axial endoskeleton ( spine ) and are cladistically and phylogenetically a subgroup of the clade Craniata (i.e. chordates with a skull ); Tunicata or Urochordata ( sea squirts , salps , and larvaceans ), which only retain the synapomorphies during their larval stage; and Cephalochordata ( lancelets ), which resemble jawless fish but have no gills or
256-420: A "hybrid formula" that specifies the parentage, or may be given a name. For hybrids receiving a hybrid name , the same ranks apply, prefixed with notho (Greek: 'bastard'), with nothogenus as the highest permitted rank. If a different term for the rank was used in an old publication, but the intention is clear, botanical nomenclature specifies certain substitutions: Classifications of five species follow:
320-503: A detailed classification within the living chordates. Attempts to produce evolutionary " family trees " shows that many of the traditional classes are paraphyletic . Hemichordates [REDACTED] Echinoderms [REDACTED] Cephalochordates [REDACTED] Tunicates [REDACTED] Craniates ( vertebrates ) [REDACTED] While this has been well known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in
384-429: A distinct head . The vertebrates and tunicates compose the clade Olfactores , which is sister to Cephalochordata (see diagram under Phylogeny ). Extinct taxa such as the conodonts are chordates, but their internal placement is less certain. Hemichordata (which includes the acorn worms ) was previously considered a fourth chordate subphylum, but now is treated as a separate phylum which are now thought to be closer to
448-567: A fast evolutionary radiation that occurred long ago, such as the main taxa of placental mammals . In his landmark publications, such as the Systema Naturae , Carl Linnaeus used a ranking scale limited to kingdom, class, order, genus, species, and one rank below species. Today, the nomenclature is regulated by the nomenclature codes . There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, and species. In addition, domain (proposed by Carl Woese )
512-436: A long time regarded as larvae of the other two groups. The other two groups, the sea squirts and the salps, metamorphize into adult forms which lose the notochord, nerve cord, and post anal tail. Both are soft-bodied filter feeders with multiple gill slits. They feed on plankton which they collect in their mucus. Sea squirts are sessile and consist mainly of water pumps and filter-feeding apparatus. Most attach firmly to
576-638: A lower level may be denoted by adding the prefix " infra ", meaning lower , to the rank. For example, infra order (below suborder) or infra family (below subfamily). Botanical ranks categorize organisms based (often) on their relationships ( monophyly is not required by that clade, which does not even mention this word, nor that of " clade "). They start with Kingdom, then move to Division (or Phylum), Class, Order, Family, Genus, and Species. Taxa at each rank generally possess shared characteristics and evolutionary history. Understanding these ranks aids in taxonomy and studying biodiversity. There are definitions of
640-399: A new rank at will, at any time, if they feel this is necessary. In doing so, there are some restrictions, which will vary with the nomenclature code that applies. The following is an artificial synthesis, solely for purposes of demonstration of absolute rank (but see notes), from most general to most specific: Ranks are assigned based on subjective dissimilarity, and do not fully reflect
704-549: A new study have shown possible affinity of these Ediacaran organisms to the ascidians. Ausia and Burykhia lived in shallow coastal waters slightly more than 555 to 548 million years ago, and are believed to be the oldest evidence of the chordate lineage of metazoans. The Russian Precambrian fossil Yarnemia is identified as a tunicate only tentatively, because its fossils are nowhere near as well-preserved as those of Ausia and Burykhia , so this identification has been questioned. Fossils of one major deuterostome group,
SECTION 10
#1732772946876768-459: A particular organism, it is usually not necessary to specify names at ranks other than these first two, within a set of taxa covered by a given rank-based code. However, this is not true globally because most rank-based codes are independent from each other, so there are many inter-code homonyms (the same name used for different organisms, often for an animal and for a taxon covered by the botanical code). For this reason, attempts were made at creating
832-466: A poor fossil record, attempts have been made to calculate the key dates in their evolution by molecular phylogenetics techniques—by analyzing biochemical differences, mainly in RNA. One such study suggested that deuterostomes arose before 900 million years ago and the earliest chordates around 896 million years ago . However, molecular estimates of dates often disagree with each other and with
896-617: A post- anal tail . In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin -like protein and inner mitochondrial membrane protease ATP23, which are exclusively shared by all vertebrates , tunicates and cephalochordates . These CSIs provide molecular means to reliably distinguish chordates from all other animals . Chordates are divided into three subphyla : Vertebrata ( fish , amphibians , reptiles , birds and mammals ), whose notochords are replaced by
960-480: A state of flux. The majority of animals more complex than jellyfish and other Cnidarians are split into two groups, the protostomes and deuterostomes , the latter of which contains chordates. It seems very likely the 555 million-year-old Kimberella was a member of the protostomes. If so, this means the protostome and deuterostome lineages must have split some time before Kimberella appeared—at least 558 million years ago , and hence well before
1024-538: A taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: There are soft constraints that separate chordates from other biological lineages, but are not part of
1088-576: A taxon in a category above the species level). It should be a natural group (that is, non-artificial, non- polyphyletic ), as judged by a biologist, using all the information available to them. Equally ranked higher taxa in different phyla are not necessarily equivalent in terms of time of origin, phenotypic distinctiveness or number of lower-ranking included taxa (e.g., it is incorrect to assume that families of insects are in some way evolutionarily comparable to families of mollusks). Of all criteria that have been advocated to rank taxa, age of origin has been
1152-440: Is a deuterostomal bilaterian animal belonging to the phylum Chordata ( / k ɔːr ˈ d eɪ t ə / kor- DAY -tə ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies ) that distinguish them from other taxa . These five synapomorphies are a notochord , a hollow dorsal nerve cord , an endostyle or thyroid , pharyngeal slits , and
1216-564: Is also called a binomial , that is, a two-term name. For example, the zoological name for the human species is Homo sapiens . This is usually italicized in print or underlined when italics are not available. In this case, Homo is the generic name and it is capitalized; sapiens indicates the species and it is not capitalized. While not always used, some species include a subspecific epithet. For instance, modern humans are Homo sapiens sapiens , or H. sapiens sapiens . In zoological nomenclature, higher taxon names are normally not italicized, but
1280-437: Is itself a chordate, and that craniates ' nearest relatives are tunicates. Recent identification of two conserved signature indels (CSIs) in the proteins cyclophilin-like protein and mitochondrial inner membrane protease ATP23, which are exclusively shared by all vertebrates , tunicates and cephalochordates also provide strong evidence of the monophyly of Chordata. All of the earliest chordate fossils have been found in
1344-467: Is not a requirement of the zoological and botanical codes. A classification in which all taxa have formal ranks cannot adequately reflect knowledge about phylogeny. Since taxon names are dependent on ranks in rank-based (Linnaean) nomenclature, taxa without ranks cannot be given names. Alternative approaches, such as phylogenetic nomenclature , as implemented under the PhyloCode and supported by
SECTION 20
#17327729468761408-423: Is not yet settled. A specific relationship between Vertebrates and Tunicates is also strongly supported by two CSIs found in the proteins predicted exosome complex RRP44 and serine palmitoyltransferase, that are exclusively shared by species from these two subphyla but not Cephalochordates , indicating Vertebrates are more closely related to Tunicates than Cephalochordates . Below is a phylogenetic tree of
1472-435: Is now widely used as a fundamental rank, although it is not mentioned in any of the nomenclature codes, and is a synonym for dominion ( Latin : dominium ), introduced by Moore in 1974. A taxon is usually assigned a rank when it is given its formal name. The basic ranks are species and genus. When an organism is given a species name it is assigned to a genus, and the genus name is part of the species name. The species name
1536-402: Is the relative or absolute level of a group of organisms (a taxon ) in a hierarchy that reflects evolutionary relationships. Thus, the most inclusive clades (such as Eukarya and Opisthokonta ) have the highest ranks, whereas the least inclusive ones (such as Homo sapiens or Bufo bufo ) have the lowest ranks. Ranks can be either relative and be denoted by an indented taxonomy in which
1600-487: Is usually associated with a certain body plan , which is also, however, an arbitrary criterion. Enigmatic taxa are taxonomic groups whose broader relationships are unknown or undefined. (See Incertae sedis .) There are several acronyms intended to help memorise the taxonomic hierarchy, such as "King Phillip came over for great spaghetti". (See taxonomy mnemonic .) Chordata And see text A chordate ( / ˈ k ɔːr d eɪ t / KOR -dayt )
1664-789: The Botanical Code , the Prokaryotic Code , the Code for Viruses , the draft BioCode and the PhyloCode all recommend italicizing all taxon names (of all ranks). There are rules applying to the following taxonomic ranks in the International Code of Zoological Nomenclature : superfamily, family, subfamily, tribe, subtribe, genus, subgenus, species, subspecies. The International Code of Zoological Nomenclature divides names into "family-group names", "genus-group names" and "species-group names". The Code explicitly mentions
1728-483: The International Society for Phylogenetic Nomenclature , or using circumscriptional names , avoid this problem. The theoretical difficulty with superimposing taxonomic ranks over evolutionary trees is manifested as the boundary paradox which may be illustrated by Darwinian evolutionary models. There are no rules for how many species should make a genus, a family, or any other higher taxon (that is,
1792-558: The PhyloCode , the code of phylogenetic nomenclature , does not require absolute ranks. Taxa are hierarchical groups of organisms, and their ranks describes their position in this hierarchy. High-ranking taxa (e.g. those considered to be domains or kingdoms, for instance) include more sub-taxa than low-ranking taxa (e.g. those considered genera, species or subspecies). The rank of these taxa reflects inheritance of traits or molecular features from common ancestors. The name of any species and genus are basic ; which means that to identify
1856-585: The echinoderms (whose modern members include starfish , sea urchins and crinoids ), are quite common from the start of the Cambrian, 542 million years ago . The Mid Cambrian fossil Rhabdotubus johanssoni has been interpreted as a pterobranch hemichordate. Opinions differ about whether the Chengjiang fauna fossil Yunnanozoon , from the earlier Cambrian, was a hemichordate or chordate. Another fossil, Haikouella lanceolata , also from
1920-412: The echinoderms , and together they form the clade Ambulacraria , the sister phylum of the chordates. Chordata, Ambulacraria, and possibly Xenacoelomorpha are believed to form the superphylum Deuterostomia , although this has recently been called into doubt. Chordata is the third-largest phylum of the animal kingdom (behind only the protostomal phyla Arthropoda and Mollusca ) and is also one of
1984-427: The fruit fly familiar in genetics laboratories ( Drosophila melanogaster ), humans ( Homo sapiens ), the peas used by Gregor Mendel in his discovery of genetics ( Pisum sativum ), the "fly agaric" mushroom Amanita muscaria , and the bacterium Escherichia coli . The eight major ranks are given in bold; a selection of minor ranks are given as well. Taxa above the genus level are often given names based on
Ocypodoidea - Misplaced Pages Continue
2048-459: The notochord is replaced by the vertebral column . It consists of a series of bony or cartilaginous cylindrical vertebrae, generally with neural arches that protect the spinal cord , and with projections that link the vertebrae. Hagfishes have incomplete braincases and no vertebrae, and are therefore not regarded as vertebrates, but they are members of the craniates, the group within which vertebrates are thought to have evolved . However
2112-418: The type genus , with a standard termination. The terminations used in forming these names depend on the kingdom (and sometimes the phylum and class) as set out in the table below. Pronunciations given are the most Anglicized . More Latinate pronunciations are also common, particularly / ɑː / rather than / eɪ / for stressed a . There is an indeterminate number of ranks, as a taxonomist may invent
2176-633: The American Ornithologists' Union published in 1886 states "No one appears to have suspected, in 1842 [when the Strickland code was drafted], that the Linnaean system was not the permanent heritage of science, or that in a few years a theory of evolution was to sap its very foundations, by radically changing men's conceptions of those things to which names were to be furnished." Such ranks are used simply because they are required by
2240-469: The Chengjiang fauna, is interpreted as a chordate and possibly a craniate, as it shows signs of a heart, arteries, gill filaments, a tail, a neural chord with a brain at the front end, and possibly eyes—although it also had short tentacles round its mouth. Haikouichthys and Myllokunmingia , also from the Chengjiang fauna, are regarded as fish . Pikaia , discovered much earlier (1911) but from
2304-494: The Early Cambrian Chengjiang fauna , and include two species that are regarded as fish , which implies that they are vertebrates. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a reasonable prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial. It has also proved difficult to produce
2368-671: The Mid Cambrian Burgess Shale (505 Ma), is also regarded as a primitive chordate. On the other hand, fossils of early chordates are very rare, since invertebrate chordates have no bones or teeth, and only one has been reported for the rest of the Cambrian. The best known and earliest unequivocally identified Tunicate is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming ( South China ). The evolutionary relationships between
2432-435: The chordate groups and between chordates as a whole and their closest deuterostome relatives have been debated since 1890. Studies based on anatomical, embryological , and paleontological data have produced different "family trees". Some closely linked chordates and hemichordates, but that idea is now rejected. Combining such analyses with data from a small set of ribosome RNA genes eliminated some older ideas, but opened up
2496-568: The cladistic exclusion of hagfish from the vertebrates is controversial, as they may instead be degenerate vertebrates who have secondarily lost their vertebral columns. The position of lampreys is ambiguous. They have complete braincases and rudimentary vertebrae, and therefore may be regarded as vertebrates and true fish . However, molecular phylogenetics , which uses biochemical features to classify organisms, has produced both results that group them with vertebrates and others that group them with hagfish. If lampreys are more closely related to
2560-475: The classification of chordates. Some chordate lineages may only be found by DNA analysis, when there is no physical trace of any chordate-like structures. Attempts to work out the evolutionary relationships of the chordates have produced several hypotheses. The current consensus is that chordates are monophyletic , meaning that the Chordata include all and only the descendants of a single common ancestor, which
2624-541: The earliest-branching chordate subphylum. The tunicates have three distinct adult shapes. Each is a member of one of three monophylitic clades. All tunicate larvae have the standard chordate features, including long, tadpole -like tails. Their larva also have rudimentary brains, light sensors and tilt sensors. The smallest of the three groups of tunicates is the Appendicularia . They retain tadpole-like shapes and active swimming all their lives, and were for
Ocypodoidea - Misplaced Pages Continue
2688-432: The family Canidae , which includes dogs, wolves, jackals, and all foxes; the next higher major taxon, Carnivora (considered an order), includes caniforms (bears, seals, weasels, skunks, raccoons and all those mentioned above), and feliforms (cats, civets, hyenas, mongooses). Carnivorans are one group of the hairy, warm-blooded, nursing members of the class Mammalia , which are classified among animals with notochords in
2752-408: The first of these synapomorphies, the notochord, which plays a significant role in chordate body plan structuring and movements. Chordates are also bilaterally symmetric , have a coelom , possess a closed circulatory system , and exhibit metameric segmentation . Although the name Chordata is attributed to William Bateson (1885), it was already in prevalent use by 1880. Ernst Haeckel described
2816-599: The following ranks for these categories: The rules in the Code apply to the ranks of superfamily to subspecies, and only to some extent to those above the rank of superfamily. Among "genus-group names" and "species-group names" no further ranks are officially allowed, which creates problems when naming taxa in these groups in speciose clades, such as Rana . Zoologists sometimes use additional terms such as species group , species subgroup , species complex and superspecies for convenience as extra, but unofficial, ranks between
2880-464: The following taxonomic categories in the International Code of Nomenclature for Cultivated Plants : cultivar group , cultivar , grex . The rules in the ICN apply primarily to the ranks of family and below, and only to some extent to those above the rank of family. (See also descriptive botanical name .) Taxa at the rank of genus and above have a botanical name in one part (unitary name); those at
2944-660: The formal definition: The following schema is from the 2015 edition of Vertebrate Palaeontology . The invertebrate chordate classes are from Fishes of the World . While it is structured so as to reflect evolutionary relationships (similar to a cladogram ), it also retains the traditional ranks used in Linnaean taxonomy . Cephalochordates , one of the three subdivisions of chordates, are small, "vaguely fish-shaped" animals that lack brains, clearly defined heads and specialized sense organs. These burrowing filter-feeders compose
3008-426: The fossil record, and their assumption that the molecular clock runs at a known constant rate has been challenged. Traditionally, Cephalochordata and Craniata were grouped into the proposed clade "Euchordata", which would have been the sister group to Tunicata/Urochordata. More recently, Cephalochordata has been thought of as a sister group to the "Olfactores", which includes the craniates and tunicates. The matter
3072-480: The gradational nature of variation within nature. These problems were already identified by Willi Hennig , who advocated dropping them in 1969, and this position gathered support from Graham C. D. Griffiths only a few years later. In fact, these ranks were proposed in a fixist context and the advent of evolution sapped the foundations of this system, as was recognised long ago; the introduction of The Code of Nomenclature and Check-list of North American Birds Adopted by
3136-468: The hagfish than the other vertebrates, this would suggest that they form a clade , which has been named the Cyclostomata . There is still much ongoing differential (DNA sequence based) comparison research that is trying to separate out the simplest forms of chordates. As some lineages of the 90% of species that lack a backbone or notochord might have lost these structures over time, this complicates
3200-434: The hierarchy of taxa (hence, their ranks) does not necessarily reflect the hierarchy of clades . While older approaches to taxonomic classification were phenomenological, forming groups on the basis of similarities in appearance, organic structure and behavior, two important new methods developed in the second half of the 20th century changed drastically taxonomic practice. One is the advent of cladistics , which stemmed from
3264-496: The level of indentation reflects the rank, or absolute, in which various terms, such as species , genus , family , order , class , phylum , kingdom , and domain designate rank. This page emphasizes absolute ranks and the rank-based codes (the Zoological Code , the Botanical Code , the Code for Cultivated Plants , the Prokaryotic Code , and the Code for Viruses ) require them. However, absolute ranks are not required in all nomenclatural systems for taxonomists; for instance,
SECTION 50
#17327729468763328-490: The most ancient taxons. Chordate fossils have been found from as early as the Cambrian explosion over 539 million years ago. Of the more than 81,000 living species of chordates, about half are ray-finned fishes ( class Actinopterygii ) and the vast majority of the rest are tetrapods , a terrestrial clade of lobe-finned fishes ( Sarcopterygii ) who evolved air-breathing using lungs . The name "chordate" comes from
3392-405: The most basic (or important) is the species, but this opinion is not universally shared. Thus, species are not necessarily more sharply defined than taxa at any other rank, and in fact, given the phenotypic gaps created by extinction, in practice, the reverse is often the case. Ideally, a taxon is intended to represent a clade , that is, the phylogeny of the organisms under discussion, but this
3456-409: The most frequently advocated. Willi Hennig proposed it in 1966, but he concluded in 1969 that this system was unworkable and suggested dropping absolute ranks. However, the idea of ranking taxa using the age of origin (either as the sole criterion, or as one of the main ones) persists under the name of time banding, and is still advocated by several authors. For animals, at least the phylum rank
3520-479: The phylum Chordata , and with them among all animals in the kingdom Animalia . Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya . The International Code of Zoological Nomenclature defines rank as: "The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at
3584-409: The possibility that tunicates (urochordates) are "basal deuterostomes", surviving members of the group from which echinoderms, hemichordates and chordates evolved. Some researchers believe that, within the chordates, craniates are most closely related to cephalochordates, but there are also reasons for regarding tunicates (urochordates) as craniates' closest relatives. Since early chordates have left
3648-455: The rank of species and above (but below genus) have a botanical name in two parts ( binary name ); all taxa below the rank of species have a botanical name in three parts (an infraspecific name ). To indicate the rank of the infraspecific name, a "connecting term" is needed. Thus Poa secunda subsp. juncifolia , where "subsp". is an abbreviation for "subspecies", is the name of a subspecies of Poa secunda . Hybrids can be specified either by
3712-653: The rank-based codes; because of this, some systematists prefer to call them nomenclatural ranks . In most cases, higher taxonomic groupings arise further back in time, simply because the most inclusive taxa necessarily appeared first. Furthermore, the diversity in some major taxa (such as vertebrates and angiosperms ) is better known that that of others (such as fungi , arthropods and nematodes ) not because they are more diverse than other taxa, but because they are more easily sampled and studied than other taxa, or because they attract more interest and funding for research. Of these many ranks, many systematists consider that
3776-468: The same rank, which lies between superfamily and subfamily)." Note that the discussions on this page generally assume that taxa are clades ( monophyletic groups of organisms), but this is required neither by the International Code of Zoological Nomenclature nor by the Botanical Code , and some experts on biological nomenclature do not think that this should be required, and in that case,
3840-410: The sea floor, where they remain in one place for life, feeding on plankton. The salps float in mid-water, feeding on plankton , and have a two-generation cycle in which one generation is solitary and the next forms chain-like colonies . The etymology of the term Urochordata (Balfour 1881) is from the ancient Greek οὐρά (oura, "tail") + Latin chorda ("cord"), because the notochord is only found in
3904-596: The start of the Cambrian 538.8 million years ago . Three enigmatic species that are possible very early tunicates, and therefor deuterostomes, were also found from the Ediacaran period – Ausia fenestrata from the Nama Group of Namibia , the sac-like Yarnemia ascidiformis , and one from a second new Ausia -like genus from the Onega Peninsula of northern Russia , Burykhia hunti . Results of
SECTION 60
#17327729468763968-485: The subgenus and species levels in taxa with many species, e.g. the genus Drosophila . (Note the potentially confusing use of "species group" as both a category of ranks as well as an unofficial rank itself. For this reason, Alain Dubois has been using the alternative expressions "nominal-series", "family-series", "genus-series" and "species-series" (among others) at least since 2000. ) At higher ranks (family and above)
4032-408: The tail. The term Tunicata (Lamarck 1816) is recognised as having precedence and is now more commonly used. Craniates all have distinct skulls . They include the hagfish , which have no vertebrae . Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or possibly all deuterostomes , are by their tails". Most craniates are vertebrates , in which
4096-674: The works of the German entomologist Willi Hennig . Cladistics is a method of classification of life forms according to the proportion of characteristics that they have in common (called synapomorphies ). It is assumed that the higher the proportion of characteristics that two organisms share, the more recently they both came from a common ancestor. The second one is molecular systematics, based on genetic analysis , which can provide much additional data that prove especially useful when few phenotypic characters can resolve relationships, as, for instance, in many viruses , bacteria and archaea , or to resolve relationships between taxa that arose in
#875124