Why do crabs roll sideways?

The quintessential crabs, that is, the brachyurans, have a relatively wide and short cephalothorax or carapace and a very small abdomen bent against the ventral surface. This morphology, which has evolved from macrura, such as lobsters and crayfish, has caused the legs to move from a longitudinal position , as occurs in macrura, to an almost radial position . That is why crabs have to move laterally, although they have no problem fully turning their body; in his defensive position he raises his body with the threatening pincers while rotating around his body, facing his enemy at all times.