Chapter:
Cnidarians

Cnidarians are a phylum of invertebrates that includes animals such as jellyfish, sea anemones, corals, and hydrozoans. They are characterized by the presence of stinging cells, called cnidocytes, which they use for defense and to capture their prey. Cnidarians have a simple body plan, consisting of a central gut cavity surrounded by tentacles. They are either sessile or free-swimming and have a life cycle that typically alternates between a sexual and asexual phase. Cnidarians play important roles in marine ecosystems as predators, prey, and as primary producers in coral reef ecosystems. In recent years, cnidarians have received increasing attention due to their sensitivity to changes in the environment, such as rising ocean temperatures and acidification, which threaten the survival of coral reef ecosystems and the numerous species they support.