The vibrant underwater world often features corals, which many people mistakenly identify as plants or even rocks. These intricate structures, however, hold a more complex biological identity. Understanding their true nature reveals a fascinating aspect of marine life. This article clarifies coral’s biological classification.
Unveiling Coral’s Identity
Coral is an animal, not a plant or a geological formation. What appears to be a single coral is typically a colony made up of thousands of individual, tiny animals called polyps. Each coral polyp possesses a sac-like body with a central mouth surrounded by a ring of tentacles. These polyps are sessile, meaning they remain fixed in one location during their adult lives, similar to how many plants are rooted.
Coral polyps acquire nutrients through two primary methods. They use their tentacles, equipped with specialized stinging cells, to capture small organisms like plankton from the water. Additionally, many corals engage in a symbiotic relationship with microscopic algae called zooxanthellae within their tissues. These algae perform photosynthesis, providing the coral with energy-rich compounds.
The Animal Kingdom Connection
Coral’s classification within the Kingdom Animalia is based on several defining biological characteristics. All organisms in Animalia are multicellular, composed of many cells. Coral polyps exhibit this multicellular organization. Animals are also heterotrophic, obtaining their food by consuming other organisms.
Animal cells lack rigid cell walls, unlike plants and fungi. Coral cells also lack these structures. While adult corals are sessile, many animals exhibit motility at some point in their life cycle, such as coral’s free-swimming larval stage. These features place coral within the Kingdom Animalia.
Introducing Cnidaria
Within the Animal Kingdom, corals belong to the Phylum Cnidaria. A defining characteristic of Cnidarians is their radial symmetry, with body parts arranged around a central axis. Cnidarians also possess specialized stinging cells called cnidocytes, used for defense and to capture prey. These cells inject venom to immobilize prey.
Cnidarians exhibit two basic body forms: the sessile polyp and the free-swimming medusa. Corals exist in the polyp form, attaching to a substrate. Other familiar Cnidarians include jellyfish and sea anemones. Within the Phylum Cnidaria, corals are further divided into groups like stony corals, which build hard calcium carbonate skeletons, and soft corals.