Chordata

The Chordata is a phylum of animals that includes the vertebrates, along with several closely related invertebrates. Members of the Chordata are distinguished by possessing at some stage of their lives a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. These features are present in the embryonic stage of all chordates and may be observed in the adult forms of some members of the group.

Characteristics

Chordates are defined by having at some point in their lifecycle the following characteristics:

• Notochord: A flexible, rod-shaped body found in embryos, which is replaced by the vertebral column in most adult vertebrates.
• Dorsal hollow nerve cord: Develops into the brain and spinal cord of vertebrates.
• Pharyngeal slits: Openings in the pharynx that may develop into gills or other structures, depending on the species.
• Post-anal tail: An extension of the body past the anal opening.

Classification

Chordata is divided into three subphyla:

• Vertebrata: Animals with backbones, which include fish, amphibians, reptiles, birds, and mammals.
• Cephalochordata: Also known as lancelets, these small marine animals closely resemble the early vertebrate ancestors.
• Urochordata: Also known as tunicates or sea squirts, these marine animals are covered with a tunic and are mostly sessile as adults.

Evolution

The earliest evidence of chordates appears in the fossil record during the Cambrian period. The phylum has since diversified into a wide range of forms, many of which are extinct. The evolution of chordates has been a subject of considerable research, and it is believed that they share a common ancestor with the phylum Echinodermata, which includes starfish and sea urchins.

Habitat and Distribution

Chordates are found in a wide range of habitats across the globe, from deep ocean floors to high mountain ranges. Their ability to adapt to various environments has been a key factor in their evolutionary success.

Importance

Chordates include some of the most familiar animals, including humans. They play various roles in ecosystems and are important for biological research due to their complex body structures and systems.

See also

• Vertebrate
• Evolution of chordates
• Phylum