Picked up this hitchhiker. When he first came into the tank two weeks ago he was blue and chunky. He moved quickly all around the tank looking for a home for several days then disappeared. I assumed my brittle star or cleanup crew ate him after missing a few days. Then I stumbled upon him attached to a bio ball below deck looking bleached and skinny. I put him back in the tank and he’s running all around again. Any idea what he is?