Button Polyps – Zoanthids
If you are looking for something easy to keep to start your journey in coral keeping the Button Polyps or Zoanthids can be a good one to start with. They are fairly hardy and will tolerate quite a range of water conditions but will do best and grow quicker under reef like conditions. They are not outwardly aggressive with tank mates but they do grow quickly and can overtake large parts of the rock work.
If you want to read up on them, here is the link to the care information on zoanthids: Zoanthids.