Heather,
It may not be dead at this point, but I was told that "bacterial infections" are common among this species in captivity. The infection literally eats away at the Linkia. My linkia was TINY, about a half dollar at best, it went quickly. When I removed it from my tank it had already dropped a limb and was falling apart, but it appeared to be holding to the glass under it's own power. In a 6 gallon tank I can't take risks like that, a dead animal in my tank means death to all inhabitants if not caught quickly. I would keep a very close eye on him. I really hope he can pull through, but I don't think there is much reversal of this infection. Keep us posted, and take more pictures as it things get better or worse...HOPEFULLY BETTER! Good luck. -DIRT