A learner makes a note: an echinoderm embryo forms the anus from the blastopore and the mouth later. The missing scientific idea is:

Deuterostomes typically form the anus from the blastopore, while the mouth forms secondarily. Echinoderms are invertebrate deuterostomes and therefore help connect invertebrate diversity with chordate evolution. This MCQ belongs to the Animal evolution topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.