Is this a type of hydroid?

[Rechelle Fleck]

I have some of these growing on the back of my overflow wall and glass. They are extremely small (about a millimeter or less). I am guess they are a type of hydroid and are they harmless?

 

[James M]

spiroid worm
Harmless filter feeder

 

[kirstyflash]

spiroid worm
Harmless filter feeder

+1