Torch corals get their most common name due to the way their tentacles flitter around in the water flow. Each polyp or head of a torch has a hard-calcified base with a fleshy top that has long tentacles growing out of it which end with a bubble on its tip. Typically, the bubble is a different color than the tentacle and as it flows in the water really resembles a torch waving in the wind.
The Duncan coral has grown in popularity in the US since it hit the scene a few years ago. Prior to that it was largely un-known to most US coral hobbyists. This was due to the export laws in Australia which prohibited the export of corals at that time. Since it is a fairly easy coral to care for, it is easy to propagate and can reproduce fairly quickly in the aquarium it has become a staple for most reefers, including the beginner.