Roller
From Sonic Retro
Roller (called "Arma" in the Japanese manual) is found in Spring Yard Zone in the Sega Genesis version of the original Sonic the Hedgehog game. They are enemies which curl in a ball and attempt to run you down. They are invulnerable at this time and can't be attacked until they stop and unfold. If they are left alone they will roll up and move off the screen. If their path of travel is interupted by a large gap they will jump over it.