ID this worm, sponge?

[tigs]

Hi all - I got these worm like creatures that are attached to the surface area of the rocks and to the shell of a hermit crab. They seem to only extend in dim light conditions. Do not notice them to be bothering anything yet, but they seem to be multiplying and spreading through out the tank. The large ones extend to about 4-5 inches. Any help would be great. Couldnt find anything useful.
thanks
Edit:In the pic below you can see the base of this creature atached to the rock.

 

[tigs]

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[tigs]

Pic of it not extended. It's about 1-3cm in length. This is a bad pic

 

[thomas712]

Looks like finger-like hydroids, In plague numbers they can be a pain in the bu tox.
http://www.rshimek.com/odd_critters.htm
about 2/3's of the way down the page.
Thomas

 

[tigs]

Q. Thanks. That's what they are. Now how to get rid of them?
edit: A. Use hot kalk paste to smother the hydriods