I'm pretty sure it's gracilaria - although there could be some room for error. I looked it up and it looked like some certain species of gracilaria (there are several, and they vary a bit in appearance) All I know is it's darn pretty and durable. Charlie up at Austin Aquarium dubbed it "dragon's breath" which I thought fit it rather well.

Tim - I can hook you up with a piece. ;)

-Mike