Chordates
Chordates (kohr-dayts)
Chordates (/ˈkɔːrdeɪts/; from Ancient Greek: χορδή, khordē, "string, cord") are a broad phylum of animals that includes the vertebrates, together with several closely related invertebrates. They are typified by having a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.
Etymology
The term "chordate" derives from the Greek khordē, meaning "string" or "cord". This refers to the notochord, a flexible rod-shaped body found in the embryos of all chordates.
Characteristics
Chordates are defined 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.
- Notochord: The notochord is a flexible rod-shaped structure that is found in the embryonic stage of all chordates. It plays a key role in the development of the nervous system.
- Dorsal hollow nerve cord: This is a hollow tube located above the notochord. It develops into the brain and spinal cord in vertebrates.
- Pharyngeal slits: These are openings in the pharynx, the part of the throat immediately behind the mouth. In fish and some amphibians, they develop into gills.
- Endostyle: This is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
- Post-anal tail: This is an extension of the body past the anal opening. It contains skeletal elements and muscles, which provide a source of locomotion in aquatic species.
Classification
Chordates are divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata. Urochordata and Cephalochordata are more closely related to vertebrates than to each other.
Related Terms
- Vertebrates: Animals that have a backbone. This group includes mammals, birds, reptiles, amphibians, and fishes.
- Invertebrates: Animals that do not have a backbone. This group includes many different types of animals, from sponges and corals to insects and mollusks.
- Phylum: A rank in the classification of organisms. It is below kingdom and above class.
- Embryo: An early stage in the development of an animal while it is in the egg or within the uterus of the mother.
- Nervous system: The complex network of nerves and cells that transmit signals between different parts of the body.
External links
- Medical encyclopedia article on Chordates
- Wikipedia's article - Chordates
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