I came down one morning to see my RFA all closed up like I’d just fed him. When I looked more closely, I saw a “little stick” poking out the top of his tentacles. Realized he was trying to eat my new tiny horseshoe crab. Since the crab was mostly all shell and he could tuck his legs up, the RFA wasn’t having much luck. I used the turkey blow him open enough to very carefully pull the crab out by his tail. Both were fine. I think the horseshoe crab got caught in the current and just landed right on the RFA who must have thought this a gift and he should eat it.
BTW, before anyone asks: DO NOT buy a Horseshoe Crab for your REEF tank! Not even if the kid at the LFS says “he’ll be fine” and that he will “just hang out at the bottom and sift around in your sand.” A Horseshoe Crab in a reef tank is kind of like an underwater kite that has broken its string. Every time he came out from under the sand, if he walked into an area with even modest flow, up he’d go, into the water column, tumbling around like a piece of flake food until I rescued him or he landed somewhere he could cling on to.