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Chordata

(Phylum)

Overview

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A phylum of animals characterized by a hollow dorsal nerve cord and, at some stage in their development, a flexible skeletal rod (the notochord) and gill slits opening from the pharynx. There are four subphyla: the Urochordata (sea squirts), Cephalochordata (lancelets), Agnatha (jawless chordates), and Gnathostomata (jawed chordates). In the Agnatha and Gnathostomata, commonly known as vertebrates or craniates, the notochord is present only in the embryo or larva and becomes replaced by the vertebral column (backbone) before birth or metamorphosis. This has permitted the vertebrates a greater degree of movement and subsequent improvement in the sense organs and enlargement of the brain, which is enclosed in a skeletal case, the cranium. In some classifications the two nonvertebrate subphyla are elevated to the status of phyla and the jawed and jawless chordates are included together in a third phylum, Craniata, containing a single subphylum, Vertebrata. The old subphyla Agnatha and Gnathostomata are then regarded as superclasses of the Vertebrata. The first chordates and the earliest vertebrates (Craniata) are both found in Cambrian rocks.

Photos

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Taxonomy

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The Phylum Chordata is a member of the Superphylum Eutrochozoa. Here is the complete "parentage" of Chordata:

The Phylum Chordata is further organized into finer groupings including:

Classes

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Acanthodii

[more]

Actinopterygii

The Actinopterygii (), or ray-finned fishes, constitute a class or sub-class of the bony fishes. [more]

Agnatha

[more]

Amphibia

Amphibians are members of the class Amphibia, a group of vertebrates whose living forms include frogs, toads, salamanders, newts and caecilians. They are characterized as non-amniote, ectothermic tetrapods, meaning their eggs are not surrounded by membranes, they are cold-blooded, and they have four limbs. Most amphibians lay their eggs in water and the larvae undergo metamorphosis from a juvenile form with gills to an adult air-breathing form with lungs. Some, however, are paedomorphs that retain the juvenile water-breathing form throughout life. Mudpuppies and olms are examples of this, retaining juvenile gills into adulthood. Adult amphibians also use their skin for respiration. [more]

Appendicularia

Larvaceans (Class Appendicularia) are solitary, free-swimming tunicates found throughout the world's oceans. Like most tunicates, appendicularians are filter feeders. Unlike other tunicates, appendicularians live in the pelagic zone, specifically in the upper sunlit portion of the ocean (photic zone) or sometimes deeper. They are transparent planktonic animals, generally less than 1 centimetre (0.39 in) in body length (excluding the tail). [more]

Ascidiacea

Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the Tunicata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide , as compared to other tunicates which are less rigid. [more]

Aves

A Class in the Kingdom Animalia.[1] [more]

Cephalaspidomorphi

Cephalaspidomorphs are a group of jawless fishes named for the cephalaspids, a group of osteostracans. Most biologists regard this taxon as extinct, but the name is sometimes used in the classification of lampreys because lampreys were once thought to be related to cephalaspids. If lampreys are included, they would extend the known range of the group from the Silurian and Devonian periods to the present day. [more]

Cephalochordata

Cephalochordata (from Greek: ?efa?? kephal?, "head" and ???d? khord?, "chord") is a chordate subphylum defined by the presence of a notochord that persists throughout life. It is represented in the modern oceans by the lancelets (also known as Amphioxus). [more]

Chondrichthyes

Chondrichthyes (; from Greek ???d?- chondr- 'cartilage', ????? ichthys 'fish') or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class). [more]

Conodonta

[more]

Elasmobranchii

[more]

Gastropoda

The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large. There are huge numbers of sea snails and sea slugs, as well as freshwater snails and freshwater limpets, and land snails and land slugs. [more]

Holocephali

[more]

Leptocardii

The lancelets (from "lancet"), also known as amphioxi, comprise some 22 species of fish-like marine chordates with a global distribution in shallow temperate (as far north as Scotland) and tropical seas, usually found half-buried in sand. They are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. In Asia, they are harvested commercially as food for humans and domesticated animals. They are an important object of study in zoology as they provide indications about the origins of the vertebrates. Lancelets serve as an intriguing comparison point for tracing how vertebrates have evolved and adapted. Although lancelets split from vertebrates more than 520 million years ago, their genomes hold clues about evolution, particularly how vertebrates have employed old genes for new functions. They are regarded as similar to the archetypal vertebrate form. [more]

Mammalia

Mammals are members of class Mammalia (), air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young. Most mammals also possess sweat glands and specialised teeth, and the largest group of mammals, the placentals, have a placenta which feeds the offspring during gestation. The mammalian brain, with its characteristic neocortex, regulates endothermic and circulatory systems, the latter featuring red blood cells lacking nuclei and a large, four-chambered heart maintaining the very high metabolism rate they have. Mammals range in size from the 30?40 millimeter (1- to 1.5-inch) bumblebee bat to the 33-meter (108-foot) blue whale. [more]

Osteichthyes

Osteichthyes (), also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes. [more]

Placodermi

Placodermi (from the Greek p??? = plate and d???a = skin, literally "plate-skinned") is a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches. A 380-million-year-old fossil of one species represents the oldest known example of live birth. [more]

Reptilia

Reptiles (Reptilia) are members of a group of air-breathing, ectothermic (cold-blooded) vertebrates which are characterized by laying shelled eggs (except for some vipers and constrictor snakes that give live birth), and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors. Modern reptiles inhabit every continent with the exception of Antarctica. Reptiles originated around 320-310 million years ago during the Carboniferous period, having evolved from advanced reptile-like amphibians that became increasingly adapted to life on dry land. Four living orders are typically recognized: [more]

Sarcopterygii

[more]

Sauropsida

Sauropsida ("lizard faces") is a group of amniotes that includes all existing reptiles and birds and their fossil ancestors, including the dinosaurs, the immediate ancestors of birds. Sauropsida is distinguished from Synapsida, which includes mammals and their fossil ancestors. [more]

Secernentea

Secernentea are the main class of nematodes, characterised by numerous and an excretory system possessing lateral canals. Like all nematodes, they have no circulatory or respiratory system. [more]

Synapsida

[more]

Thaliacea

The Thaliacea comprise a class of marine animals within the subphylum Tunicata. Unlike their bottom-dwelling relatives the ascidians, thaliaceans are free-floating for their entire lifespan. The group includes both solitary and colonial species. [more]

At least 70 species and subspecies belong to the Class Thaliacea.

More info about the Class Thaliacea may be found here.

Bibliography

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Footnotes

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  1. http://www.ubio.org/browser/details.php?namebankID=21646

Sources

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Last Revised: October 03, 2013
2013/10/03 15:43:42