Pillar Coral.

I sort of arbitrarily picked this species of coral, just because I've never posted a coral. And they are probably among the most magnificent animal types that exist. Also, one of the most important for ecosystem health. People often forget they are animals, because they don't 'move.' They actually do -- they spawn, and on some occasion will extend tissue and eat other coral. Typically they just take in debris. They also have a polyp stage in life, similar to jellyfish. They attach to a surface eventually, and grow from there.

This specific species grows up to 8 feet tall and lives along the Atlantic coasts.
Perhaps most interesting about these (and other) corals is that they can produce sexually as well as asexually. They are also hermaphroditic. So they have both sperm and egg, and can also reproduce by just budding and creating a new coral pillar. Which is why they tend to cluster in large groups.

Unlike most animals, since corals form a geographical structure, they serve a function similar to that of trees in a forest -- they provide nooks for animals and homes for teaming wildlife. They also affect the amount of oxygen and carbon in the water, which is obviously important to any living creature around. And like plants, there are plentiful examples of fish that associate with specific types of coral, both in coloration and in behavior (think: bees or flowers and orchids). They also provide color - a visual masterpiece that compels us to love the seas.

Here's a video to help you learn more about coral reproduction: