Black corals are named for the dark color of their skeletons. Branching and spiny, the skeleton is typically shaped like a tree that can be as tall as a man. Its trunk anchors the black coral to reefs, shipwrecks, or other hard surfaces. A protein (antipatharin) gives the skeleton its strength. For centuries, people have been harvesting black coral. Pieces of skeleton are cut and polished into shiny beads for jewelry in coastal countries. Asian markets sell black coral amulets and diving rods that are thought to ward off evil and sickness. Early Hawaiians ground black corals into a medicinal powder. Recent research has shown that chemicals extracted from black corals have potential as anti-cancer drugs. Black corals tend to live in the deep sea, making harvest dangerous. As it has become rare in locations that are easier to access, the value of black coral has gone up.

Anthozoans (anemones and corals) have stem-like bodies that anchor to the ocean body or other surface. Tentacles radiate like petals around the top of the stem (anthozoa flower animals). Both their bodies and tentacles are hollow, opening into a mouth in the center of the flower. Anemones and corals capture food with their tentacles and push it into their mouths. While they mostly eat small, floating food (plankton), stingers (nematocytes) on their tentacles allow some anthozoans to consume larger prey (even fish or crabs) by stunning them first. Food travels from the mouth to the hollow space inside their bodies, where it is digested. Since they have only one opening, waste products are expelled back out their mouths. Some anthozoans benefit from a relationship with unicellular algae (mutualism). While the coral provides a safe place for the algae to live, the algae makes food by photosynthesizing.