Cnidaria

Cnidaria is a phylum of aquatic animals, including jellyfish, corals, sea anemones, and hydras. Its members possess specialized stinging cells called cnidocytes.

Cnidocyte: A specialized cnidarian cell that fires a capsule, often delivering a toxin or sticky thread. This defining cell gives the phylum its name and enables prey capture and defense.
Cnidocyte discharge: The rapid firing of a cnidocyte's capsule and thread in response to mechanical or chemical cues. This specialized discharge captures prey and deters predators.
Coral reef: A marine ecosystem built largely from the calcium-carbonate skeletons of reef-forming corals. Colonial cnidarians create habitat for a large diversity of marine life.
Ctenophora: A phylum of marine animals commonly called comb jellies, propelled by rows of cilia. Comb jellies resemble jellyfish but belong to a separate animal phylum.
Animal phylogeny: The evolutionary history and branching relationships among animal lineages. Cnidarian placement among early-diverging animals informs reconstructions of animal origins.
Nematocyst: A pressurized capsule inside a cnidocyte that rapidly ejects a thread. It is the best-known stinging apparatus housed within cnidocytes.
Planula: A ciliated, free-swimming larval stage in the life cycle of many cnidarians. Planula larvae disperse before settling and developing into the next body form.
Coral reef restoration: Interventions intended to help damaged coral reefs recover or persist. Restoration efforts focus on ecosystems built by reef-forming cnidarians.
Porifera: The animal phylum of sponges, which filter water through porous bodies and lack true tissues. Sponges provide a comparison with cnidarians' organized tissues and nerve cells.
Cnidarian nervous system: A decentralized network of neurons found in cnidarians, without a centralized brain. Its organization raises questions about how nervous systems evolved before centralized brains.

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