What are all these black worms?

[fearoflemmings]

I am two weeks into cycling my life rock. Yesterday I noticed thousands of these little black worms. Most are one maybe two millimeters long, are round and black.

 

What are they? Should I be concerned? The rock is from Tonga and the sand was 'dead', so they must have come from the rock.

[Steve973]

Are they moving around? And do they have little "hairs" on them or anything? They might be baby bristle worms. Can you get a closeup or macro shot of them?

 

Steve

[nano-nemo]

if you dont like them get a sand sifting star, they eat them