Please help identify mystery creature in Sump

[stevoiii]

These things look like flat worms which I have had in the past but they seem to large to be worms. Also they are like "shells" for something to hatch instead the actual creature/bug. They seem hollow when you feel them. Does anyone know what these are? Thanks for your help in trying to figure out what these are.

 

[kfisc]

Looks like sycon- or pineapple sponges. Every tank I've had gets them; they're completely harmless.

 

[thegrun]

Looks like sycon- or pineapple sponges. Every tank I've had gets them; they're completely harmless.

+1

 

[Misled]

Agreed, hey grun.