Help identifying please

[Lookabill]

These white guys are on the back of my tank and all over in my sump (looks like some sort of filter feeder). They are stationary... looks like a single head...there are alot in the sump! My instinct is that they are ok, or even good?

When I was getting a pic of the above I saw another critter...white as well, but moves a bit like a slug....what is that?

Thanks so much!!

 

[DSC reef]

Pineapple sponges and flatworms. The clear are usually no concern and are lod eaters. Typically go away on their own.

 

[Salty Lemon]

Here is a hitchhiker ID Guide that @Crabs McJones posted. I go back to it frequently and found it to be a good reference for basic critter information. https://www.reef2reef.com/threads/what-is-that-a-r2r-guide-to-common-new-tank-hitchhikers.443382/

 

[Crabs McJones]

Ghost Flatworms and Pineapple Sponges