my pearly oyster blister pearl

I found this seashell as i was walking along the beach. I picked it up as you rarely find these sort of shells as a whole. As i looked inside (unfortunately i split in two), cleaned it up and saw, what appears to me a lump attached to the inside of the shell that i thought to be a pearl. I have tried to look it up to identify it, but, i am getting nowhere, could you tell me if it is just a common thing or if it is a formation of a pearl?

Anyway, it is sitting pretty on my bathroom shelf, and makes for an interesting original piece of natural art! Also are you able to tell me how to preserve it as its looking rather dry and looks if it could deteriorate.

Many thanks.