Small crabs?

[1fastrock]

Hello everyone I just noticed these in my aquarium this morning and was wondering if anyone could tell what they are. Or even if they are helpful or hurtful.

 

[Joshua2598]

Spribobid worm I believe. Butchered the spelling.

 

[1fastrock]

Thanks for the quick answer! Are they harmful or hurtful and where do they come from??

 

[Joshua2598]

Harmless hitchhiker. Can grow out of hand like in my tank and might grow on/irritate corals when they get out of hand. Check if the moved if they haven't then they are spriobib worms