At first Aseroe rubra looks like a lizard's egg, but about half the size of a chicken egg. The star shaped anemone structure grows out of the egg and can appear overnight.
The arms, always in pairs, are red and arise from a central disk covered in a foul smelling olive green to black mucilage, which seems very attractive to flies. The centre of the anenome structure is quite hollow, with the hollow seeming to extend down the full length of the white stype.
It stands about 40mm high and is about 40mm across. A look alike is Clathrus archeri, which has the spore mass centred on the arms.