Most starfish have eyes on the tips of their arms. They’re hard to see and even if you spot them, you might not recognise them as eyes. But they can see you (as long as you’re not moving too fast).

The starfish in the top image is an Indo-Pacific species called the blue star (Linckia laevigata). Here’s a close-up of one of its arms. That groove runs up the entire underside of the arm and contains thousands of tube feet, which the animal uses to crawl about. The eye sits at the end of the groove, where the white arrow is pointing.

It’s a tiny red nub, barely half a millimetre wide. It’s usually exposed, but the starfish can retract it