cnidáriák

Cnidaria is a phylum of aquatic animals that comprises the jellyfish, corals, sea anemones, and hydras. These organisms are characterized by their radial symmetry and the presence of specialized stinging cells called cnidocytes. Cnidarians are found in marine and freshwater environments worldwide.

The cnidarian body plan is typically a sac-like structure with a single opening that serves as both mouth and anus. There are two primary forms in the cnidarian life cycle: the polyp, which is sessile and attached to a substrate, and the medusa, which is free-swimming and bell-shaped. Many cnidarian species exhibit alternation of generations, with both polyp and medusa stages present in their life cycle.

Cnidocytes contain nematocysts, which are coiled, harpoon-like structures that can be discharged to capture prey or for defense. These stinging cells are a defining feature of the phylum. Cnidarians are carnivorous, feeding on small invertebrates and plankton, which they immobilize with their cnidocytes.

The phylum Cnidaria is divided into several classes, including Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. Hydrozoans include freshwater hydras and some jellyfish. Scyphozoans are the true jellyfish, characterized by a dominant medusa stage. Cubozoans, or box jellyfish, are known for their cube-shaped medusae and potent venom. Anthozoans, such as sea anemones and corals, lack a medusa stage and exist only as polyps. Corals are significant reef-builders, forming complex ecosystems that support a vast diversity of marine life.