Implicating Arachnid -> Arthropod.
Reason: "Arthropoda (from Greekἄρθρον árthron, "joint", and πούς pous (gen.podos), i.e. "foot" or "leg", which together mean "jointed leg"), and include the insects,arachnids, and crustaceans" http://en.m.wikipedia.org/wiki/Arthropod