They're a common polyp. Some people call them daisy polyps, daisy cloves, mat's polyps, starburst polyps, eight tentacle cloves/polyps. They are NOT Pipe Organs.
I have them growing randomly in my tank as well, they're a pinkish/brown color, right?
Keep an eye on them, they do grow quickly and can overgrow other corals. I have to frag mine at least once a month.
They look like this:
or this: