Actually its very simple, you compare the cowbox's gonio and mine, you will notice the difference espcially the tentacles.
But personally, Goniopora is not a coral I will recommend, I prefer the Alveopora, they are hardier and also much pleasing to the eyes. The difference between Alveo and Gonio is in the tentacles - Alveo have 12 tentacles per polyp while the Gonio have 24.
I dun have a good pix of the Alveo right now, anyway the Alveo is on the top right hand of this photo next to the Trachiphyllia.