Acan Lords tend to be more "fleshy" in appearance with clear seperation between polyps, where as Acan Echinatas appear to share their fleshy mantles. The pics you posted are Lords, this pic (which I hijacked from the "interweb") is of an Echinata, you can see how the polyps tend to blend into one another rather than seeming to "stand alone" as is seen in your Lord pics.
-Dave
Edit: I should note here that I am no expert, but I believe this is a good rule of thumb.