I posted a photo of a Megalodon tooth on the thread on Craftster, so I thought I'd post something living here:
That is a lookdown, which used to be the logo for the Aquarium. (Now it's a sea turtle.) They're very shiny and very flat. You can find them all over the Atlantic coasts, from Canada to Uruguay (including the Gulf of Mexico). People don't eat them, for the most part; they're mostly used for aquariums because they're a little unusual-looking and do fairly well in captivity.
This is a teeny one that is living in the tank next to the touch tank, where they keep urchins and horseshoe crabs and things like that. When they get bigger, I think they move to the Chesapeake Bay tank next door, which had lookdowns bigger than my face. (This one is probably the size of my palm.)
We have a few more adventures to go, because the send deadline has been extended to Valentine's Day. I'm hoping PB will get to see some snow, but we haven't had any yet. Plus, on Wednesday, we're going down to the beach. I realized last night that we had NO oceanfront pictures! We'll fix that, though.