ok, this thread just makes me angry...
....first of all, krans could not have blood.... at all. Everything that you could possibly think of would erode it from the inside out. Sand, being made of grains of rock, if flowing through the krans\' \"veins\" would surely wear it down to nothing. The stupid comment of lava, would just melt it out-right. Gas would cause it to crack and break. Water would just wear it down.
.... so sadly, as much as you all are going to hate it, krans can only be answered in that hated phrase \"\'Tis Magic!!\". It\'s an MMORPG, so frankily, I don\'t think anyone would care much. So I suggest all of you who spent so much wasted time here trying to come up with scientific explainations for a fantasy game to sit down, and look at your life, and ask yourself \"What the hell am I doing?\". Because fantasy is supposed to escape logic, and make no sense, because it contains magic. With what you are proposing, there would be no point of krans, they would either be the strongest, or weakest of races. To go with a scientific explanation, they would be extremely weak... vulnerability to the elements, vulnerability to magic, bashing bludgeons, and slicing swords, with krans having a slow regeneration rate, they would have extremely short life-spans, and be completely horrible to play.
However, to go with fantical explinations would be as equally bad... fire-breathing, rock-hard, impenetrable walking fortresses? C\'mon, that just plain isn\'t fair...
So I say just leave them as humanoids with a \"durable\" shell-like skin.
P.S. I, myself am a kran