What does it mean to be a deuterostome

an animal whose mouth develops from a second opening in the early embryo, opposite to the initial opening blastopore of the rudimentary gut. Chordates and echinoderms are deuterostomes.

Deuterostomia is a subtaxon of the Bilateria branch of the subkingdom Eumetazoa, within Animalia, and are distinguished from protostomes by their deuterostomic embryonic development; in deuterostomes, the first opening (the blastopore) becomes the anus, while in protostomes, it becomes the mouth.