Why does the spider family bear the name Arachnida?

Ages ago,people believed there was magic in the weaving of a spider's web and the Greeks told a story about girl, Arachne,who was to give all spiders the name of Arachnida. One day,Arachne,who was skilled in the art of weaving,challenged the goddess to a contest. She proved herself better than Athene at the craft and that immortal goddess,jealous and enraged that a mere mortal should defeat her, changed Arachne into a spider, eternally doomed to weave her web with the thread spun from her own body.