Perhaps it was a bonellid worm proboscis? Although I didn't think they were white. They live in holes in either live rock or in the substrate, and use a Y-shaped proboscis to find food.
There are also Terebelliadae worms, often called spaghetti worms; they have white feeding tentacles but they aren't branched. Cirratulid spp. are called hair worms, and they put out both gills and feeding tentacles, but aren't white and aren't branched.
Of course, micro/mini britle stars will often hide in live rock or in the substrate and feel around for food w/ a leg or two. But, again, these legs aren't segmented/branched.
Eunice spp. do have pinchers on its jaws, but you likely would have seen the head of the animal as well. They do live in holes, however.
You may want to check out those things. If you are looking for an inexpensive group of books to purchase that go over various animals, I can suggest two.
The first is Microcosm/TFH's (publisher) pocket expert series. There are two books, one for marine fish and one for marine invertebrates. Marine fish is by Scott Michael, who is very well known and well respected. This book is like a slimed down version of the 8 volume Reef Fish series that he is writing. Marine invertebrates is by Ronald Shimek, also well known and respected. I believe new editions of each have been released, and each costs about $20.00
The other series is from Barron's (publisher.) They don't always produce the best material for hobbyists, but they have two books out by Tristan Lougher called What... that are a big improvement on what you usually find from Barron. They aren't quite as scientific as Michael's and Shimek's books, but they are decent overviews. I have "What marine fish?" and "What invertebrates?" They are subtitled "a buyer's guide for marine aquariums." Each was approx. $15.00
