What's this worm?

[Mariette]

I'm sure I've seen em on here in my daily snoopings but I can't remember what they're called. I believe they're harmless. Just need a name if possible. There are 2 in the pic. W 2 little white stringy things sticking out.
Anyone?

 

[squaretwelve]

Looks like spionid worm.

Spionid worm | Melev's Reef

This interesting critter is found in most reef tanks near the rockwork or in the substrate of the refugium. The worm (possibly a Chaetopterid or Spionid) secretes a mucous to build a small tube with sand grains (two tubes visible in this image), and extends two 'palps' for feeding. The worm...

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