In general terms, thats the simplest explaination. In casual conversation, most term zoas as the small, Solomon Island style polyps, while larger polyps, like RPEs are called palys. Scientifically, they are not palythoa, but when referring to 'Zoos' or 'Palys', RPEs are referred to as palys. We were just discussing the need for a more formal listing on Club-Zoa recently, showing scientific name, then breaking down to the common 'name', then showing the color morph variations within that common 'name'. I think zoaid may be headed in that direction. Who Dah has a great site going.
Larry