Sun polyp is a silly store name anyways =0P Orange cup coral, dendro, tubinaria. All the same really they just branched out in the dendrophylliid family. Kinda like when you call a rainbow monti a pokerstar monti.
when calling something a sun polyp, usually means the ones on the top right while when talking about a dendro it usually means bottom right or the single larger polyps your talking about. Sun polps usually grow as a colony although each mouth is a separate organism, growing from the base skin of the tube usually. While the dendro's tend to spawn reproduce, often growing heads sometimes an inch or two between. All depending on species. Thats roughly what i remember from when i did my research when i was into sun polyps and dendro's.