In fact I’m certain it’s a plant. If you teased out clavularia or a cousin on a slide for a pic like that, it would never fragment like it does in the bottom portions
that isn’t even showing correct polyp morphology like oral opening or digestive tracts, bi pinnate fronds missing i can see meristem growth pattern at the tips
ive never seen a low growing morph like that, rest assured someone who does marine planted tanks will buy it