When you kill the Mutant Enderman, he will spawn those and they will suck you in (if you are too close). They will damage you and explode on contact, but not if you left-click one before it explodes. The fragment will follow you and give you the Endersoul Hand if you drop an Eye of Ender on the ground (with this guy following you)!

NOTE: THE FRAGMENT WILL DISAPPEAR AFTER THE HAND IS CLAIMED