The deep-sea Dumbo octopus was spotted a mile below the surface of the Pacific Ocean, close by an unnamed seamount in the Papahānaumokuākea Marine National Monument.

There was much to celebrate: The 18-person team had just discovered the fourth known deep-sea octopus nursery in the world—as well as possibly a new species. The other three nurseries exist off ...

Why do octopus punch fish? Science has a compelling theory. Octopuses in the Red Sea often hunt together with other predatory fish—and sometimes hit them.