Murex
I am not sure what kind of Murex these shells are. My best guess is Chicoreus brunneus ガンゼキボラ. They are a bit worn, but the hermit crabs love them. Amami 2023
This one shows a little more detail. They were all lined up on the beach in the shade of the rocks. Amami 2023
A Hermit Crab in a (Chicoreus sp.) shell. I think it could be a Chicoreus torrefactus センジュモドキ. Amami 2025
Same shell as above on the beach. Amami 2025