Leather Coral "worm"?

I have noticed on two seperate leather corals what I am assuming is a worm with exceptionally long "tentacles". At night, a long pair of very fine streamers is cast out that looks like a one-sided feather. There was a pair coming off a small toadstool that were about 5" long. Yesterday I purchased a large cabbage leather about 8" in diameter and have just noticed a pair of these same tentacles emerging from the leather and these are over a foot long and the 'feather' portion is about an inch wide. What are these, is it anything to be concerned about, and is it just coincidence that two leathers have had them now or do they seem to host them more than others?

Thanks