Easy to differentiate!
Acan Echinata is an evil little brat that kills everything and doesn't have very defined separation between polyps (they look like chalices to me).
Acan Lordhowensis no longer exists and is now Micromussa Lordhowensis, has defined polyps, and isn't an Acan at all.
There is one other Acan. Grand Acan or something like that. I don't know much about them. I'd be interested to hear how they differ as well.