Japanese vintage Takotsubo (octopus trap pot)

Octopus trap

Many barnacle and a shell are stuck in a pot because it was in the sea for a long time.

In Japan, the Mediterranean, and other regions, an ancient variant is used to catch octopuses. They are usually heavy earthenware pots, and do not have an inverted funnel. These traps are left on the sea floor for days at a time. Octopuses enter and remain inside, using the pot as shelter and protection. No bait is used. When the pot is raised, the octopus will not normally try to escape. (wikipedia)