Hitchhiker id on live rock

[HereFishyFishy3]

Can someone please help me figure out what this is? It’s slightly transparent and reminds me of some type of sponge. It will inflate and deflate every so often. Thanks!

 

[EeyoreIsMySpiritAnimal]

No idea what I'm looking at/for.

 

[ISpeakForTheSeas]

I'm assuming you mean the black blob in the center of the photos? The pics are a bit too dark to really tell. If it inflates/deflates, doesn't move around, and doesn't have any tentacles, my first thoughts would be some kind of sponge or tunicate. Generally tunicates look more mucousy or leathery than sponges do, so if it's mucuosy or leathery looking, that'd be my guess, but better pics definitely wouldn't hurt with the ID process.