Chordate

A chordate is an animal in phylum Chordata, defined by a notochord present at least during embryonic development. Chordates also share a dorsal hollow nerve cord, pharyngeal slits, an endostyle or thyroid, and a post-anal tail at some life stage.

Dorsal hollow nerve cord: A hollow nerve cord running along the dorsal side of chordates. This chordate structure develops into the central nervous system of vertebrates.
Gastrulation: An early developmental process that reorganizes an embryo into germ layers and establishes body axes. Chordate tissues and body axes are established through this embryonic reorganization.
Cephalochordate: A marine chordate, such as amphioxus, that retains a notochord from head to tail throughout life. Cephalochordates preserve a relatively simple version of the chordate body plan.
Pikaia: An extinct, Cambrian animal known from the Burgess Shale and often classified as an early chordate. Its fossils preserve features used to investigate early chordate evolution.
Hemichordate: A marine deuterostome animal with a pharyngeal region and a stomochord, but no true notochord. Its similar anatomy helps distinguish chordate traits from shared or convergent features.
Pharyngeal slit: An opening or groove in the pharynx, present in chordates at some developmental stage. Its varied forms in chordates include feeding structures and vertebrate gill passages.
Neurulation: The embryonic process that forms the neural tube from ectoderm. It produces the dorsal hollow nerve cord characteristic of chordates.
Tunicate: A marine invertebrate chordate whose free-swimming larva typically has a notochord and nerve cord. Tunicate larvae show chordate traits that are reduced in most adults.
Haikouichthys: An Early Cambrian fossil animal commonly interpreted as an early vertebrate. It provides evidence about the early diversification of vertebrate chordates.
Echinoderm: A marine deuterostome animal, such as a sea star or sea urchin, with a water vascular system. Echinoderms share deep ancestry with chordates but lack the chordate body plan.

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