Insects belong to the class Hexapoda (or Insecta), meaning 'six legs.' Defining features include: three pairs of jointed legs, three body segments (head, thorax, abdomen), one pair of antennae, and usually wings. Diplopoda = millipedes (two pairs of legs per segment); Chilopoda = centipedes (one pair per segment); Arachnida = spiders, scorpions (four pairs of legs).