It's not from outside the tank. I've been finding pieces of it since I added a torch coral, a plate coral and 2 Trochus snails 4 months ago on an occasional basis , I have a feeling it hitched a ride inside a Trochus snails shell is my best guess. I totally forgot to bring it with me to my LFS but I got a starfish and 2 nassarius snails hehe.Umm that’s a bug part that fell in your tank..
I am keeping it in a jar so I can show my LFS guy but he imports some stuff that is taken directly from the ocean so who knows.