What are these little guys just found them

[Seadogs12]

Was looking around and saw these guys and can’t figure out what they are or if there good or bad

 

[Tahoe61]

Looks like a type of harmless feather duster, Spirorbid.

 

[penfold2]

Not spirorbids, which have a uniformly coiled snail-like tube and are only 2-5mm, but definitely some kind of feather duster. They're filter feeders and do not multiply prolifically or harm other inhabitants. I love tiny feather dusters, especially the colored ones like this.