GIANT-CUP and an ELEPHANT EAR mushrooms

Can anyone tell me the differences between these two corals? I placed my name on an E-MAIL alert with BlueZoo Aquatics for an elephant ear coral...RHODACTIS MUSSOIDES. And they list separately a giant cup mushroom...AMPLEXDISCUS SPP. The elephant ear they list as 'semi aggressive', and the giant cup as 'aggressive'. Looking them up there seems to be a lot of overlapping between the two, with confusing info. My concerns are with which one will be O.K. with small fish without trying to eat them. I was comfortable with it being the elephant ear till I'm seeing all the confusion out there. Does any one know the difference between the two so I can tell for sure which I'm getting, or if neither will be safe around my small gobies? Or does any one know of another mushroom that grows ridiculously large that is safe around small fish? Thanks for any help,

Hack