Just because they are both arthropods (phylum) does not mean that a crab is a spider. Crabs are in the Malacostraca class which also includes shrimp and lobsters (which is part of the Crustacea subphylum) whereas spiders are in the Arachnida class which is part of the Chelicerata subphylum which includes horseshoe crabs (but are not in Arachnida).
SerperiorThanU posted...
I'm arachnophobic yet I love crabs and eating them
Lucky for you, crabs are not arachnids. As demonstrated above, crabs only share the same phylum or subphylum as spiders.