anthozoans

Anthozoans are a class of marine cnidarians that includes sea anemones, stony corals, soft corals, and sea pens. In contrast with many other cnidarians, anthozoans are sessile as adults and display polyp morphology throughout life, with no medusa stage in their life cycle. Individuals range from solitary to colonial, often forming reefs or benthic structures in suitable habitats.

Anthozoans possess a gastrovascular cavity with a single opening serving as mouth and anus, and they are equipped with nematocyst-bearing stinging cells (cnidocytes) for prey capture and defense. Their body plan is radially symmetric, usually with numerous tentacles arranged around the mouth. In many species, the body wall secretes calcium carbonate to form a rigid skeleton, as seen in stony corals, while soft and some other forms have either flexible or absent skeletons.

Many anthozoans harbor symbiotic dinoflagellates, zooxanthellae, within their tissues. The mutualistic relationship supplies photosynthates that support growth and reef-building in light-rich environments, while zooxanthellae receive protection and access to waste products. Reproduction occurs sexually, via external or internal fertilization with planula larvae, or asexually through budding and fragmentation to form new polyps or colonies. Some species reproduce by broadcast spawning, releasing gametes into the water in synchronized events.

Anthozoans are exclusively marine and inhabit a range from shallow, sunlit waters to deep, cold seas. Reef-building corals (hard corals) contribute substantially to three-dimensional habitats, supporting diverse communities. Across the group, anthozoans are threatened by climate change, ocean acidification, pollution, and destructive fishing practices, which contribute to coral bleaching and reef degradation.

Taxonomically, Anthozoa is divided into major lineages such as Hexacorallia (sixfold symmetry; hard corals and some anemones) and Octocorallia (eightfold symmetry; soft corals, sea fans, and sea pens). The class contains both solitary and colonial forms and exhibits a wide range of life histories and morphological adaptations.