Not really. Most cultured mysis are small and perfect for newly hatched cuttles (that usually start feeding in the first week after hatching). Amphipods are generally too strong for newly feeding cuttles and often get away even when caught.
Do they look transparent at all? If you gently touch them, they should feel like they have water inside of them. If they feel hard like they have jello inside of them, they are bad. You could hang on to them for awhile longer, maybe they will inflate. If they start disintegrating, then they are dead.