This animal was living. It was living inside a shell. It was the color Black and could scoot around on the sea floor.
Barbuda Island.
These two shells (both paired) were a nice surprise as the tide was coming in after several rewarding hours of shelling. The 1st I have seen outside of Florida, and the larger one, at 34mm, is the largest I have seen (apparently they can reach 40mm).
This spot, Beachwalker County Park, is consistently excellent for seashells of all sizes and other marine life. It is also the only public beach access of Kiawah, but well worth a visit.