Honeycomb Oyster (Hyotissa hyotis) シャコガキ also Zigzag Oyster
The Honeycomb Oyster is large and usually cemented to the bottom. They look like they were made for Halloween. Amami
The Honeycomb oyster is usually heavily encrusted. Amami
The shell of the Honeycomb Oyster is said to be soft like styrofoam. Amami