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The twilight zone is a layer of the ocean. It is between the surface and deep zones. The twilight zone reaches from 660 to 3,280 feet (200–1,000 m) below the surface. This zone gets little or no light. The water there is cold. Japanese spider crabs spend most of their time in the twilight zone.

To molt, the crab’s inner body separates from its hard shell. After a few weeks, a new thin shell forms underneath. Then the crab is ready to shed the old shell. The crab takes in seawater. The water makes the crab swell like a balloon. Eventually, the old shell cracks. The crab pushes its body out of this opening.

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Making Connections


Have you ever seen an animal with an exoskeleton? What kind of animal was it?


Have you read books about other animals that live on the ocean floor? How do those animals find food?


Scientists still haven’t learned everything about Japanese spider crabs. Why do you think the crab’s habitat makes it hard to study?

Teacher Resources

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