What are these ?

[GSnake]

They're snail like , but have these filament things. A type of Spirobid worm?

 

[ReeferHD]

spirorbid worm, not sure why they're clustered like that though.

 

[MoshJosh]

Looks like they are right under the gyre pump? . . . I assume they dig the flow/get blasted with food right there?

 

[Cthulukelele]

When I had my leopard who loved tube worms they clustered in areas like that because that's just where they wouldn't get eaten. That'd be my guess.