My neighbor was chargrilling some oysters one time a few years ago, and I got a fresh one from him that I put in the sump. It had been iced down but recovered and opened up a bit. It lived for a couple of days, but I think the icing took its toll. That or my system not being adequate for it.
I've taken snails and hermit crabs, even a sand dollar, and put them in the tank. The snails have done fine, though on occasion have eaten an astrea or two. The hermit crabs get too big and crabby.
Anyway, I relate all this because it is unorthodox by today's standards, but maybe not in the past.