we have seen a lot of these on our beaches here in South Carolina and I've looked everywhere to find out what they are with no luck
It's a pretty cool creature, whatever it turns out to be. I at first thought it might be some kind of cowry like the Coffee Bean Trivia, but I found some live photos on line and they didn't look the same.
I also wondered if it could be something like these corals just described by Anna DeLoach in the Pacific that have a symbiotic worm that pulls them around: http://blennywatcher.com/2012/04/28/walking-coral/
I will watch with interest to see if someone comes up with an answer.
REEF Headquarters | P.O. Box 246 | 98300 Overseas Hwy | Key Largo, FL 33037 | USA Phone: 305-852-0030 | Fax: 305-852-0301 | email: firstname.lastname@example.org