I've got crabs! (What are they?)

[Blizz003]

I'm fairly certain it's some kind of mythrax. . It looks just like the emerald but with different colours. I recently added two cardinals and 1 bicolour angel. The cardinals are doing well but I think the angel got ick from the sress of moving tanks. He was fine at the LFS and when I first put him in my tank he seemed super happy, exploring everywhere and inspecting the snails and crabs... But then two nights later he was on his side up against the glass breathing really heavy. He also has some orange spots on the yellow part of his head and along his gills which is what makes me think ick... He'll swim up next to the crabs until they pick at his skin, poor guy. I don't have a hospital tank and I'm not sure what to do. Will neon gobies help or do I need to medicate the poor fellow? Before you ask, the water parameters are all good and he still eats mysis. Ahhh poor thing he just started rubbing against the rocks I feel so bad...