It is Phlyctenactis tuberculosis; it comes out at night, and separates it for floating, crawling and climbing for hunting and food at night. This small sea creature is connected to the rock, seaweeds, seawater and algae till the day ... its marvels being done by the sea, it is also known as the swimming or wandering anemone.
SOURCE - https://www.treehugger.com/