Here's why:
* Deuterostome development: The term "deuterostome" refers to the way these animals develop their first opening during embryonic development. The blastopore, the first opening, becomes the anus, and the mouth forms later.
* Contrast with protostomes: Protostomes, on the other hand, develop their mouth from the blastopore, while the anus forms later.
Examples of deuterostomes:
* Echinoderms (starfish, sea urchins)
* Chordates (humans, fish, birds)
So, deuterostomes develop both a mouth and an anus, but they form in a different order than protostomes.