Why are spiders classified as arthropods?

Spiders are among the most numerous type without vertebrates, it is called: Type of arthropods. Spiders have articulated limbs, and also a hard chitinous cover, for a spider it is like a skeleton and a shell. Among arthropods, the spiders themselves belong to the class (Arachnids). Spiders have four pairs of paws, other insects have three pairs, there are other insects like (scolopendra) or, it is also called a flycatcher, a centipede, which has more than four pairs of paws. There are other classes that include scorpions, hayfields, and others.