Octi and fireworms 

I found a "new" Octi's home, just ten meters from the catamaran, at a depth of about two meters. I located it by the shell remnants that it discarded after eating the contents. Among the shells, in addition to rapana, there was also one cowrie shell.
It turns out that "fireworms" parasitize on octopuses. Of course, not in the direct sense. From time to time, the octopus cleans its shelter, sweeping out debris with the remnants of its meals. The worms sit by the entrance and wait for this moment. I've even noticed that they crawl from quite a distance to the entrance to check if there's anything tasty.