Disc or Lettuce Coral (Turbinaria mesenterina)
Coconut Garden, Lembeh.
I have corrected sp based on appearance here:
http://www.coralsoftheworld.org/species_factsheets/species_factsheet_summary/turbinaria-mesenterina/
Still tentative.
"Turbinaria mesenterina", commonly known as disc coral, is a species of colonial stony coral in the family Dendrophylliidae. It is native to the Indo-Pacific region. The International Union for Conservation of Nature has rated its conservation status as being "vulnerable".
Similar species: Stony Corals
Uploaded Aug 8, 2018. Captured May 13, 2018 10:06 in Unnamed Road, Pasirpanjang, Lembeh Sel., Kota Bitung, Sulawesi Utara, Indonesia.