Eye of the krill
The tiny Antarctic krill has a complex compound eye.
The Antarctic waters of the Southern Ocean contain about 300 or 400 trillion Antarctic krill (Euphausia superba). By sheer mass (approximately 500 million tonnes), these tiny crustaceans, which feed on microscopic phytoplankton, may be the most abundant single species on the planet.
They weigh up to 2 grams apiece, can be up to 6 centimetres in length, and live for as long as 6 years. The swarms they live in can contain as many as 30,000 individuals per cubic metre. Every two or three weeks, they shed their exoskeletons and grow new ones.
They identify phytoplankton to snack on with their compound eyes, much like those of an insect