seashells

So i went to the beach the other day and when i was there i picked up some shells that caught my eye. Some with barnacles on, some are muscle shells, other mollusk shells and also parts of a crab carcass. (shown in picture) Is there anything i must do to be able to add them to my tank?

I have live sand in all 3 DTs. I need to provide some "variety" for a few fish and so I've gotten some fine sand that is for SW and made a few piles of it. They like it. But I would like to add 2 other things but I'm not sure if it's ok. 1. I bought a canister of shell pieces. It appears to be...