Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Mollusks, annelids, and arthropods are protostomes. Echinoderms and chordates are deuterostomes. This distinction is important. Why does it matter? It shows that echinoderms are more closely related to chordates than are the other invertebrate phyla. This is not apparent based on other, more obvious traits. Answer: protostomes
Output:
Mollusks, annelids, and arthropods are considered what?