Eyes Spider

this jumping spider s main ocelli (center pair) acute. outer pair secondary eyes , there other pairs of secondary eyes on sides , top of head.

spiders have 4 pairs of eyes on top-front area of cephalothorax, arranged in patterns vary 1 family another. principal pair @ front of type called pigment-cup ocelli ( little eyes ), in arthropods capable of detecting direction light coming, using shadow cast walls of cup. however, in spiders these eyes capable of forming images. other pairs, called secondary eyes, thought derived compound eyes of ancestral chelicerates, no longer have separate facets typical of compound eyes. unlike principal eyes, in many spiders these secondary eyes detect light reflected reflective tapetum lucidum, , wolf spiders can spotted torch light reflected tapeta. on other hand, jumping spiders secondary eyes have no tapeta.

other differences between principal , secondary eyes latter have rhabdomeres point away incoming light, in vertebrates, while arrangement opposite in former. principal eyes ones eye muscles, allowing them move retina. having no muscles, secondary eyes immobile.

some jumping spiders visual acuity exceeds factor of ten of dragonflies, have far best vision among insects; in fact human eye 5 times sharper jumping spider s. achieve telephoto-like series of lenses, four-layer retina , ability swivel eyes , integrate images different stages in scan. downside scanning , integrating processes relatively slow.

there spiders reduced number of eyes, of these six-eyes numerous , missing pair of eyes on anterior median line, others species have four-eyes , two. cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.