A member of the phylum Cnidaria, zoanthid coral is a colonial anemone closely related to single anemones. Zoanthid coral, including members from the species Palythoa and Zoanthus, have some characteristics we associate with plants and some with animals. They grow in the ocean as a group, permanently attach to reefs, feed like anemones, and propagate like coral.
Cnidarians are radially symmetric, which means they are shaped like a series of cylinders that could be rotated without being able to determine which side is the "front." Zoanthid coral grows in a colony, which means a bottom mat connects many tubules. Each tubule, called a stolon, resembles a single anemone. A top section has a ring of short tentacles surrounding its central mouth. This top is held up by an elongated column of tissue like the stalk of a mushroom, and this in turn connects to the collective mat.
Colonies can be made up of dozens of such stolons, each 1 - 1.5 inches (2.5 - 3.8 cm), to form carpets on or around reefs. Zoanthid coral prefer to grown on pieces of broken off coral that collect in valleys on tidepools or the ocean floor, but they can also survive on sand and rocks. Zoanthid coral grows in seemingly disparate ways. Some stolons are male and female, and release sperm and eggs to get fertilized and grow into a whole new colony. However, an existing colony can also propagate by branching off new polyps, like coral, that start from the carpet and grow upwards.
Zoanthid coral, since it can't perambulate (move around), feeds off nutrients that drift through the current, called detritus. Detritus is miniature pieces of food other creatures don't even notice, like bits of algae, plankton, or waste. Other nutrients are extracted from photosynthetic algae that live on zoanthid coral, called zooxanthellae. However, zoanthid coral is also equipped with poisonous toxins that can sting other creatures from the tips of their tentacles. This is solely for protection, not to paralyze animals for food.
Medical researchers are interested in zoanthid coral because it has symbiotic relationships with animals and plants, like algae and crabs, yet maintains production of toxic chemicals. Although the toxins are poisonous to the nervous system, they might be able to benefit humans against disease.