Spiders are invertebrates with a two part body (phalo thorax and abdomen), biting chelicerae and silk glands that discharge through spinnerets. They have 4 pairs of legs and additional pair of short appendages (pedipalps) beside the chelicerae. Eight is not only the number of legs spiders have. The original spiders and most still have eight eyes and if that is not enough spiders still live today which have the original complement of eight spinnerets.