Chordate

Chordatachordatesnerve cordprotochordatechordate animalschordate phylumolfactoresproto-chordatetextvertebrate
A chordate is an animal of the phylum Chordata.wikipedia
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Dorsal nerve cord

nerve corddorsaldorsal hollow nerve cord
During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum.
The dorsal nerve cord is a unique feature to chordates, and it is mainly found in the Vertebrata chordate subphylum.

Animal

Animaliaanimalsmetazoa
A chordate is an animal of the phylum Chordata.
The Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes, arthropods, and molluscs—and the deuterostomes, containing both the echinoderms as well as the chordates, the latter containing the vertebrates.

Notochord

notocordembryonic notochord cells
During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum.
If a species has a notochord at any stage of its life cycle, it is, by definition, a chordate.

Pharyngeal slit

pharyngeal slitspharyngeal bars
During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum.
Pharyngeal slits are filter-feeding organs found in vertebrate chordates.

Fish

fishesfinfishichthyofauna
Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds, and mammals); Tunicata or Urochordata (sea squirts, salps); and Cephalochordata (which includes lancelets).
They form a sister group to the tunicates, together forming the olfactores.

Ambulacraria

Coelomopora
The Chordata and Ambulacraria together form the superphylum Deuterostomia. Hemichordata (which includes the acorn worms) has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates.
The Ambulacraria are part of the deuterostomes, a larger clade that also includes the Chordata, Vetulicolia and Saccorhytus.

Phylum

phyladivisionsuperphylum
A chordate is an animal of the phylum Chordata. The Chordata and Ambulacraria together form the superphylum Deuterostomia.

Coelom

coelomic fluidacoelomatepseudocoelomate
Chordates are also bilaterally symmetric; and have a coelom, metameric segmentation, and a circulatory system.
Examples of deuterostome coelomates belong to three major clades: chordates (vertebrates, tunicates, and lancelets), echinoderms (starfish, sea urchins, sea cucumbers), and hemichordates (acorn worms and graptolites).

Echinoderm

Echinodermataechinodermsechinoids
Hemichordata (which includes the acorn worms) has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates.
The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles).

Vertebral column

spinespinal columnspinal
Cladistically (phylogenetically), vertebrates – chordates with the notochord replaced by a vertebral column during development – are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs.

Metamerism (biology)

metamericmetamerismmetameric segments
Chordates are also bilaterally symmetric; and have a coelom, metameric segmentation, and a circulatory system.
Humans and other chordates are conspicuous examples of organisms that have metameres intimately grouped into tagmata.

Neural tube

neural canalneural canalsdorsal neural tube
In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord.

Olfactores

The Craniata and Tunicata compose the clade Olfactores.
Olfactores is a subphylum within the Chordata that comprises the Tunicata (Urochordata) and the Vertebrata (sometimes referred to as Craniata).

Vetulicolia

Vetulicolidavetulicoliansvetulicolian
There are also extinct taxa such as the Vetulicolia.
Therefore, it can be concluded that vetulicolians are crown-group chordates and probably the sister group of modern tunicates.

Lancelet

amphioxusAmphioxiformeslancelets
Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds, and mammals); Tunicata or Urochordata (sea squirts, salps); and Cephalochordata (which includes lancelets).
The lancelets, also known as amphioxi (singular, amphioxus), consist of about 30-35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes.

Vertebrate

Vertebratavertebratesvertebral
Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds, and mammals); Tunicata or Urochordata (sea squirts, salps); and Cephalochordata (which includes lancelets). Cladistically (phylogenetically), vertebrates – chordates with the notochord replaced by a vertebral column during development – are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
Vertebrates comprise all species of animals within the subphylum Vertebrata (chordates with backbones).

Body plan

bauplanBody formbodyplan
The history of the discovery of body plans can be seen as a movement from a worldview centred on the vertebrates, to seeing the vertebrates (or chordates) as one phylum's body plan among many.

Craniate

Craniatacraniatespreoccupied
Cladistically (phylogenetically), vertebrates – chordates with the notochord replaced by a vertebral column during development – are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage.

Agnatha

jawless fishagnathanjawless vertebrates
Agnatha (Ancient Greek ἀ-γνάθος "no jaws") is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species.

Taxonomy of invertebrates (Brusca & Brusca, 2003)

(see Brusca and Brusca)Brusca and BruscaTaxonomy of invertebrates

Conodont

conodontsConodontaconodont element
Conodonts (Greek kōnos, "cone", + odont, "tooth") are extinct agnathan chordates resembling eels, classified in the class Conodonta.

Cambrian explosion

Cambrian radiationCambrian invertebratesCambrian transition
Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago.
Most of the phyla featured in the debate about the Cambrian explosion are coelomates: arthropods, annelid worms, molluscs, echinoderms, and chordates – the noncoelomate priapulids are an important exception.

Ascidiacea

ascidianascidianssea squirt
Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds, and mammals); Tunicata or Urochordata (sea squirts, salps); and Cephalochordata (which includes lancelets).
As a general rule, the larva possesses a long tail, containing muscles, a hollow dorsal nerve tube and a notochord, both features clearly indicative of the animal's chordate affinities.

Hemichordate

HemichordatahemichordatesSaccoglossus kowalevskii
Hemichordata (which includes the acorn worms) has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates.
A hollow neural tube exists among some species (at least in early life), probably a primitive trait that they share with the common ancestor of chordata and the rest of the deuterostomes.

Endostyle

During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum.
Since the endostyle is found in the three branches of chordates, it is presumed to have arisen in the common ancestor of these taxa, along with a shift to internal feeding for extracting suspended food from the water.