Unidentified Marine Organism Discovered Near Corfu Shoreline

While snorkeling near Ipsos, Corfu, I found this floating between the rocks, ~5 m from the shore. I later found a few more growing underneath a rock, leading me to believe that one died/ got dislodged. They were between 5-15 cm long, and the diameter of the tentacles was maybe 2 cm. It's quite firm to the touch.