The name refers to which end of the animal the “tube in a tube” digestive tract appears during embryogenesis. Deuterostomia, (Greek: “second mouth”), group of animals classified together on the basis of embryological development and by molecular criteria. During development the mouth of deuterostomes develops from an opening into the embryonic gut other than the blastopore, which develops into the anus.

In protostomes, the blastopore is developed into the mouth whereas in deuterostomes, the blastopore is developed into the anal opening.

Deuterostomes represent a major branch of Animalia as do protostomes. Most of the animals with exoskeletons would be protostomes while those with endoskeletons are deuterostomes.

A number of deuterostomes have distinctive larval forms. The Deuterostomia constitute one of two divisions of the coelomates (animals having a coelom).

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