Friends or foes?

[tchat]

First reef tank! Found from my TBS live sand. I think the shelled one is a bivalve. Wondering about the worm and snail though. It’s silly how much I’m enjoying these tiny boring creatures but so cool finally having something alive in the tank haha.

 

[keagan]

The top two are a cerith snail and a juvenile peanut worm but I can't tell what I'm looking at in the last picture.

 

[Gumbies R Us]

@ISpeakForTheSeas

 

[EricR]

Third one is likely a lancelet:
TBS Hitchhikers - Lancelets