In the Photic Zone: Flower Animals
Life on the Rocks by Juli Berwald.
While there are many different sorts of Anthozoa, their basic unit is a polyp: an individual soft flower-animal similar to an anemone. While anemones are solitary, in corals these polyps band together to form colonies. As they grow, they build a skeleton of limestone around themselves, drawing calcium and carbon molecules from the seawater. They also draw in carbon dioxide to feed their resident algae. Over time these skeletons accumulate upwards and outwards. Corals build on their predecessors, leaving their own legacy behind them for the next generation. Reefs are, in part, the frozen exuberant bouquets of the past.
Boomers Daily 