Common Names
Cnidaria includes a wide variety of species commonly known by names such as jellyfish, sea anemones, corals, and hydras. These common names often reflect the distinct forms and habitats of the species within this phylum.
Characteristics
Cnidarians exhibit a range of physical forms but share several key characteristics. They possess radial symmetry and a simple body structure that consists of a gastrovascular cavity. This cavity functions both as a stomach and a circulatory system. Cnidarians have two primary forms: the sessile polyp and the mobile medusa. Polyps, such as sea anemones and corals, are typically attached to a substrate, whereas medusas, such as jellyfish, are free-swimming.
A unique feature of Cnidarians is their cnidocytes, cells that contain specialized organelles known as nematocysts. Nematocysts are used to capture prey and for defense, ejecting a harpoon-like structure that can deliver toxins to potential threats or prey.
Environments
Cnidarians inhabit a wide range of aquatic environments. Coral species are often found in shallow tropical and subtropical oceans, where they form extensive and biodiverse coral reefs. These reefs provide essential habitats for many marine species. Jellyfish and hydras can be found in various aquatic settings, from coastal waters to the deep sea. Some species are adapted to live in extreme environments, such as the deep ocean or brackish waters.
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