Chordate

Chordate

Chordate (/ˈkɔːrdeɪt/), from the Greek khordē, meaning "string" or "cord", is a broad phylum in the Kingdom Animalia that includes a large number of diverse organisms.

Etymology

The term "chordate" is derived from the Greek khordē, which translates to "string" or "cord". This is in reference to the notochord, a flexible rod-shaped structure that is found in the embryonic stage of all chordates.

Definition

Chordates are characterized by having, at some stage in their life cycle, a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. Chordates are also bilaterally symmetrical, have a coelom, possess metamerism, and have a circulatory system with a heart that is dorsal, hollow, and single.

Classification

Chordates are classified into three subphyla: Urochordata, Cephalochordata, and Vertebrata. Urochordata and Cephalochordata are more commonly referred to as "invertebrate chordates", while Vertebrata includes the larger and more complex vertebrate animals.

Urochordata

Urochordates are marine invertebrate animals, consisting of about 3,000 species, including the sea squirts, salps, and larvaceans. They are characterized by a notochord and a nerve cord in the larval stage, which disappear or are reduced in the adult form.

Cephalochordata

Cephalochordates are small, "primitive" marine animals that include the lancelets or amphioxus. They possess a notochord, nerve cord, and numerous gill slits, and are considered close relatives of the vertebrates.

Vertebrata

Vertebrates are the largest group of chordates, with over 60,000 species. These include fish, amphibians, reptiles, birds, and mammals. Vertebrates are characterized by a vertebral column or spine, and a large, well-developed brain.

Related Terms

• Notochord
• Pharyngeal slits
• Endostyle
• Post-anal tail
• Bilateral symmetry
• Coelom
• Metamerism
• Circulatory system
• Urochordata
• Cephalochordata
• Vertebrata

External links

• Medical encyclopedia article on Chordate
• Wikipedia's article - Chordate

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