Possibly a Sea Urchin? (Gulf of Thailand)

[huskychemist]

I spotted this critter on a snorkel at Koh Sak, in the Gulf of Thailand a few weeks ago.

I don't happen to have my ID books at work right now...but I recall a sea urchin that looks similar to this in one of my books...but the sea urchin in the book has more "hair" than the critter in my picture.

Any thoughts?

Many thanks!

 

[LeslieH]

It's the exoskeleton of a heart or biscuit urchin. The reason why there's no spines is because the animal is dead & all the spines have fallen off.