What is this ?

[aggrofish]

Found this on the back glass, small about 1/4”.it appears to be turning stab it with a knife?

 

[xxkenny90xx]

Asterina starfish. The population will explode and alot of people really like them. But they eat my zoas so I relocate them to my fish only tank

 

[4tanks]

It's an asterina star fish you can remove or leave some people do some don't . there are some that may munch on corals I personally never had a problem and leave them the funny shape is due to it braking a peice of and reproducing

 

[aggrofish]

Thanks. First time I saw it. I bought some small live rock that was covered in coralline to seed the tank must have been on there.