What is this?

[KQuillan]

Just saw this tonight. What is it?

 

[AFHokie]

Looks like an urchin

 

[WheatToast]

Looks like an urchin

+1
Assuming the hitchhiker isn't "squishy," my guess is that this is a small Echinometra rock-boring urchin:
https://www.liveaquaria.com/product/3080/shortspine-urchin?pcatid=3080&c=530+3080&s=ts&r=

 

[KQuillan]

Oh wow, interesting. Thanks for the info.

 

[AydenLincoln]

+1
Assuming the hitchhiker isn't "squishy," my guess is that this is a small Echinometra rock-boring urchin:
https://www.liveaquaria.com/product/3080/shortspine-urchin?pcatid=3080&c=530+3080&s=ts&r=

Squishy lol that they aren’t. Don’t be shy touch it!