What it was
A hunter about half a meter long, twice the length of a dinner plate, swimming in the ocean about 514 million years ago. Flexible flaps ran down each side, and two spiny arms at the front curled in around soft prey.
Its name means "strange shrimp," because its arms and its mouth were first found separately and named as different animals.
The eyes
Each eye held at least 24,000 tiny units, in a fossil eye about three centimeters across. Early trilobites had about a hundred lenses each.
Still a mystery
A fossil eye keeps the lenses but not the brain. So we know it could see sharply, but not how clever it was.