Common name Anemone.
About When prey such as a small fish or a shrimp touches the tentacles they quickly wrap around grabbing the victim which is then paralysed with the sting of the tentacles. When you touch the anemone you can't feel the sting as it is unable to pass though the skin of fingers. They can also take dead material that passes their way by the good grace of the currents and waves.
Food goes in an out of the same hole. They can move around to find more favourable locations.