Given a scientific passage and an answer, generate a question for the given answer.
--------
Question: Passage: Monarch butterflies gather in large groups as they migrate 2,500 miles south each fall. They return to the north in the spring. This migration is a cycle that repeats every year. Answer: migration

Answer: What do we call the seasonal movement of animals?

Question: Passage: In this equation, the letters A and B represent the reactants that begin the reaction, and the letter C represents the product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs. Answer: reaction mechanism

Answer: What term is used to describe the sequence of elementary steps that together comprise an entire chemical reaction?

Question: Passage: Mollusks are mainly aquatic invertebrates in Phylum Mollusca. They include snails, squids, and clams. Mollusks have a coelom and several organ systems. Most also have a shell, head, foot, and radula, which is a feeding organ. Mollusks are either free-living heterotrophs or parasites. Answer: mollusca

Answer:
What phylum includes snails, squids and clams?