Assuming these have more than just the two super long tentacles, I'd guess either a Spaghetti Worm or a Hair Worm, both of which are harmless/beneficial:
Looks like either a hair worm (Cirratulidae) or a spaghetti worm (Terebellidae) to me - if the tentacles all come out from a single point, it’s a spaghetti worm; if they come out from basically all over the body it’s a hair worm.