technically "sun corals" and dendros both come from the family "Dendrophylliidae" so one could argue that sun corals are also "dendros"
my point is that they are very closely related species (Tubastrea aka "sun corals" and Dendrophyllia aka "dendros"), and there are also many undescribed species...
Odds are that it's a sun coral (aka Tubastrea species), it's hard to say without more growth