Can anyone identify what this is?

I would now say they are ball spunges and there looks to be 3 peanut worms in one of the pic #2 or could be small polups the wild ones. The yellow stuff is eithere spunge or coriline algae. coriline algae is not always purple there is a gray, skin color, red, orange , green and yellow by the looks of yours. All good. Purple coriline algae comes in different types the standard and plating. The purple is what most hobbiest want as it is nice but I like a veriety with mostly purple. sponges come in all colors black, purple, blue, orange, yellow, red, white, green and pink. I do like ball spunges as they change as they get older.

Bill

[ScubaGirl]

Thank you for the replies. Been a mad frenzy of googling the last few days. I've been learning tons from you guys.

[ScubaGirl]

Found a couple more of these things. I apologize, the first pic is not the greatest (it's in a cave) and I had to use a flashlight making them more yellow than they actually are. The second one is quite different than the others in my tank. The original ones that I posted before all look the same, they haven't changed a bit.

[Wayne]

Those above look like sponges to me Any healthy system will have them.