I've had this coral (sun coral/tubastraea) for a few weeks now and really enjoy it. This coral requires some involvement since it's not photosynthetic and each polyp requires frequent feeding.
It typically opens up only at night or when I feed it (the following pics were taken at about 2am, I had to briefly turn on some of the lights for these shots):
There are at least three smaller sun corals not attached to main colony (two can be seen on the right). They're growing among some black sun coral which are attached to the same piece:
More black sun coral pics:
In this final pic the polyp on the bottom left is finishing up the last of the mysis shrimp:
It typically opens up only at night or when I feed it (the following pics were taken at about 2am, I had to briefly turn on some of the lights for these shots):
There are at least three smaller sun corals not attached to main colony (two can be seen on the right). They're growing among some black sun coral which are attached to the same piece:
More black sun coral pics:
In this final pic the polyp on the bottom left is finishing up the last of the mysis shrimp: