Stationary tentacle or worm, nocturnal, rapidly shrinks in bright light to what basically just looks like a pebble of sand stuck in a some snail slime.
Edit: not sure the video is going to work so here are stills
Vermetid snail and considered a nuisance. Based on where it is located, your best recourse is to place a dab of gel superglue from the dollar store right over the opening and it will starve and be gone
Definitely looking like digitate hydroids to me, not vermatid snails. Thank you both for your quick responses. I will most likely try covering them up with superglue.