All members of the Cladocera group possess a single black compound eye (with a few exceptions) attached by a muscle that controls it. During embryonic development, the organism has two eyes that merge together to create a single one! The dark colour of the eye is due to the presence of accessory pigments like melanin that hide the actual photoreceptive pigment which is a nearly colourless purple. 

Cladocerans tend to flee strong light or be attracted by it when the intensity is reduced. It has been shown that the muscles that control the eye movements also transfer the stimulus to the antennae muscles which are responsible to change the direction of the body.

Cladocerans like Daphnia can detect polarized light, UV light and coloured light! Light reflected by algae and other food particles is polarized and strongly attracts Daphnia. Different species of cladocerans have also shown to be attracted by different colours (so different wavelengths). Most of them are strongly attracted to orange light while some prefer green, blue or violet!