Known as flower animals, these ancient marine predators build the world's most diverse ecosystems.

Nature · Published 3 October 2026 Swipe more like this →

In short: Anthozoa, or flower animals, are a massive group of marine invertebrates including corals and sea anemones. Unlike their jellyfish relatives, these creatures spend their adult lives anchored to the seabed, using stinging tentacles to capture prey. They are the silent architects behind the planet's most vibrant and productive underwater reefs.

The class Anthozoa, a major branch of the phylum Cnidaria, has a fossil record stretching back 550 million years to the Vendian period. While many cnidarians like jellyfish cycle through a free-swimming medusa stage, anthozoans are exclusively polypoid. As adults, they remain sessile, attached to the seabed, though they begin life as free-floating larvae that drift to new settlements. Their body plan, characterized by radial symmetry, features a central mouth surrounded by stinging tentacles called nematocysts, which can deliver toxins or use sticky surfaces to ensnare prey.

Anthozoans are divided into two primary groups based on their symmetry: Hexacorallia and Octocorallia. Hexacorallia includes stony corals, which secrete calcium carbonate skeletons to form the massive structures of reefs, as well as sea anemones and zoanthids. In contrast, Octocorallia—which includes soft corals, sea fans, and sea pens—typically exhibits eight-fold symmetry and lacks the heavy calcified skeletons of their stony cousins. Instead, they often rely on internal structural supports that allow them to sway gracefully with ocean currents.

Beyond their structural role, these animals are biological powerhouses. Many species host microscopic algae called zooxanthellae within their tissues, gaining energy through photosynthesis. This relationship is vital for reef-building corals, which occupy less than 0.1 percent of the ocean yet harbor one in every four known marine species. These ecosystems act as essential nurseries for juvenile life and provide a critical buffer against coastal erosion. Furthermore, the organisms found within these reefs have become a frontier for pharmaceutical research, offering compounds that show potential in treating conditions ranging from asthma to cancer.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• True jellyfish are ancient, cup-shaped predators that have thrived since the Cambrian period.
• Hydrozoa are tiny, predatory architects that build complex, interconnected living colonies in the sea.
• The Pacific sea nettle is a drifting predator with a golden, venomous armament
• The polyp is a master of survival, anchoring life across half a billion years.
• Nettle cells built jellyfish, corals, and anemones
• Despite their cerebral appearance, brain corals are ancient, slow-growing architects of the ocean floor.
• The stinging secret of nature's most primitive tissue-based animals
• The ancient biological blueprint of stinging, radial symmetry
• Simple sea creatures may hold the secret to the first eyes
• The tiny, armored architects of the ocean's hidden biodiversity
• Are these deep-sea predators a single animal or a complex, living colony?
• These glowing, quill-shaped colonies are actually sophisticated, multi-polyp organisms anchored in the deep sea.

More in Cnidarians · More in Nature · Latest · A–Z · All topics