Jumping spiders have eight eyes, the two large ones in the centre-and-front position (the anterior-median eyes, also called "principal eyes") providing acute vision and housed in tubes in the head.
The other six are secondary eyes, positioned along the sides of the carapace and acting mainly as movement detectors.
While the middle pair of secondary eyes in most jumping spiders are small, those of Phaeacius and other members of the sub-family Spartaeinae are almost as large as the other secondary eyes.
Although other spiders can jump, salticids including Phaeacius have significantly better vision than other spiders, and their main eyes are more acute in daylight than a cat's and 10 times more acute than a dragonfly's.
The main eyes focus accurately on an object at distances from approximately 2 centimetres (0.79 in) to infinity, and in practice can see up to about 75 centimetres (30 in).

Spiders, like other arthropods, have sensors, often modified setae (bristles), protruding through their cuticle ("skin") for smell, taste, touch and vibration.
Unlike insects, spiders and other chelicerates do not have antennae.
Jumping spiders have eight eyes, the two large ones in the centre-and-front position (the anterior-median eyes, also called "principal eyes") providing acute vision and housed in tubes in the head. The other six are secondary eyes, positioned along the sides of the carapace and acting mainly as movement detectors. While the middle pair of secondary eyes in most jumping spiders are small, those of Phaeacius and other members of the sub-family Spartaeinae are almost as large as the other secondary eyes. Although other spiders can jump, salticids including Phaeacius have significantly better vision than other spiders, and their main eyes are more acute in daylight than a cat's and 10 times more acute than a dragonfly's. The main eyes focus accurately on an object at distances from approximately 2 centimetres (0.79 in) to infinity, and in practice can see up to about 75 centimetres (30 in).
Spiders, like other arthropods, have sensors, often modified setae (bristles), protruding through their cuticle ("skin") for smell, taste, touch and vibration. Unlike insects, spiders and other chelicerates do not have antennae.
Phaeacius