There probebly Vermetid gastropod, They use those "spider webs" like a fishing rod... they launch it all over the place and then "reel" it back in and eat whatever is stuck on it. and thats JMO maybe someone else here has another idea. A pic would help though.
. Anyways do a google image search on Vermetid gastropod and you'll see right away if its what you got.
Marc...
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20Gal, 45 lbs LR, 65W PC 10 000K + 65W PC 20 000K + 10Gal sump/fuge
Livestock :hermit and snails, Green star polyps, Button polyps, Finger leather, Xenia, Zoanthids, Mushrooms, Yellow polyps, montipora digitata, acropora, ?mistery polyps?, mistery crab, six line wrasse
tube growth on rock 
