Any idea what these are??

[ricky stubbs]

Evening all can anyone give me insight as to what these are ??I have just removed my skimmer and the back of my tank is full of these little things??
Any idea what they are?? Are they bad for my tank

 

[Brad Miller]

Typical stuff.
Looks like pineapple sponges and the small white things are Spirorbid Worms...all harmless filter feeders

 

[tripdad]

They look like pineapple sponges, harmless.

 

[ricky stubbs]

OK brilliant thank you

 

[Richard Hercher]

The free clean up crew you never knew you had

 

[sfin52]

They look like pineapple sponges. The white circular thing is a spionid worms . good guys