Deuterostome

A deuterostome is an animal belonging to Deuterostomia, a clade that includes chordates, echinoderms, and hemichordates. Its name comes from a common embryological pattern in which the blastopore develops into the anus.

Deuterostomia: A major animal clade comprising chordates, echinoderms, and hemichordates. The clade name denotes the evolutionary group to which every deuterostome belongs.
Radial cleavage: An embryonic cleavage pattern in which cell divisions produce tiers aligned above one another. It is a traditional early-development feature associated with many deuterostomes, not all of them.
Cambrian explosion: A geologically brief interval of rapid animal diversification beginning about 539 million years ago. Early fossils from this interval provide evidence about the emergence of major deuterostome lineages.
Protostomia: A major bilaterian clade that includes ecdysozoans and lophotrochozoans. It is the sister grouping traditionally contrasted with Deuterostomia.
Blastopore: The opening formed during gastrulation, when an embryo begins organizing its germ layers. Its developmental fate gave deuterostomes their name, though it is not a universal diagnostic trait.
Indeterminate cleavage: Early embryonic cell divisions in which separated cells can retain the capacity to form a complete embryo. This developmental tendency is often contrasted with determinate cleavage in protostomes.
Pikaia: An extinct, soft-bodied animal from the Middle Cambrian Burgess Shale, often interpreted as an early chordate. Its fossils are among the classic early records used to discuss chordate history.
Ecdysozoa: A protostome clade whose members grow by shedding an external cuticle. Its arthropods and nematodes show why protostome diversity cannot be reduced to one simple body plan.
Gastrulation: An early embryonic process that rearranges cells into germ layers and establishes body organization. The traditional distinction between deuterostomes and protostomes concerns events during this process.
Enterocoely: A mode of coelom formation in which pouches bud from the embryonic gut and become body cavities. It is a classic developmental pattern described for several deuterostome groups.

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