There are at least 35,000 species of spiders, but scientist think there are many more not yet discovered. Spider classifications are the three main groups that the species fit under. There are primitive spiders, tarantulas and relatives, and true spiders.
Spiders grow by shedding their skeleton and replacing it with a bigger one.
This process is called molting. Their skeleton is a hardened, non-living exoskeleton, which protects the spider from danger.