actually, i think it's a s. serenei. you can tell from the extra spacing of the polyps towards the middle and the definite/regular flattish edges between the upward ridges.
sarcos come in a variety of shapes and colors depending on species, age, and environment/history. so you can have a yellow sarco in a toadstool format (especially when they're young/frag). you can better determine species as they grow though and take their adult/mature forms.