Let me introduce you to one of my favorites, Belle. Belle is a 'sheet' or 'plate' coral, and lives very deep, 108 feet, 30 m,,,see the blue tinge of the deep blue sea in the photo?, the surrounding bottom is grayish white when you're there looking at it. This is in Cane Bay here on St. Croix, in the Caribbean Sea. Called sheet or plate because this coral is very thin, this is, umm, like a pizza crust spread out over the rock below. The hole, or dent, is where Belle's polyps lost out a fight with a 'wire' coral, a type of black coral, that looks like--- a wire. See it? Belle is more than three feet, a meter, across. Quite large, and well more than a hundred years old.
This is a photo, correct colors, taken from about a foot, thirty centimeters, away. The specific type of coral, Latin named, is decided by the placement of the corralites, polyps, the wonderful little white stars. I love them so much!!! Another type of plate coral has the polyps on top of the ridges. And another has the ridges sharp, and meeting into little shapes, with the coral polyps inside.