The little guy is a common octopus (octopus vulgaris) that was caught in a crab trap in Florida Keys. I work at a Marine research facility and sea turtle rehabilitation center in Ponce Inlet, FL called the Marine Science Center. He was donated to us for research purposes. He is housed in a 120 gallon aquarium with various corals, as well as a Walking Batfish, Slipper Lobster and a few small blennies and damselfish all collected from Ponce Inlet. We feed him live shrimp and fiddler crabs, though he surprisingly doesn't bother the blennies or damselfish.
Very interesting creature, but also very shy. The previous picture was the best one I've ever been able to capture, as he tends to hide in his cave most of the day.