Button Coral - Cynarina lacrymalis

"Cynarina" is a genus of stony coral in the family Lobophylliidae. It is monotypic and the only species in the genus is "Cynarina lacrymalis". It is variously known as the flat cup coral, the solitary cup coral, the button, doughnut or cat's eye coral. It is found in the western Indo-Pacific Ocean and is sometimes kept in reef aquaria.