This listing just appeared in Coins & Paper Money > Coins: US > Dollars > Mixed Lots. I dunno -- pretty sure these have been cleaned, and I suspect they spent some time in salt water.
I don't know if you're being serious or not. But it's a flat kind of sea urchin. When they die they look kinda cool so people collect them.
These are most likely plastic fakes. anyway. This shows yet again that eBay is a great place to exploit the massively stupid.
Many thanks, I thought it was some sort Dollar variety, being in the UK there is a lot of terms you use in the USA that even after 40 years of coin trading I'm not familiar with. I did a bit of diving and collected sea urchins to soak in bleach and use the shells for decoration.