cnidocytesspecialized

Cnidocytes are specialized cells of cnidarians, a group that includes jellyfish, corals, sea anemones, and hydras. These cells play a central role in prey capture and defense by housing the cnidae, a diverse suite of intracellular organelles. The most well known cnidae are nematocysts, which are capsules that fire a thread-like filament when stimulated.

Each cnidocyte contains a capsule (the cnidocyst) and an inverted tubule. A sensory structure called the cnidocil acts as a trigger on the cell surface. When stimulated by mechanical contact or chemical cues, the cnidocyst discharges rapidly, everting the tubule and delivering toxins or adhesive secretions into the target. Discharge occurs extremely fast, among the fastest cellular processes in nature.

Cnidae come in several forms. Nematocysts are the most common and highly diverse, capable of penetration, entanglement, or adhesion, often delivering venom that can immobilize prey or deter predators. Spirocysts, found in some hydrozoans and sea anemones, secrete sticky filaments rather than venom and help secure prey. Ptychocysts are a specialized type in some tubeworms associated with cnidarian hosts. The overall cnidome, or complement of cnidae types, varies among species and life stages.

Cnidocytes originate from multipotent interstitial cells within the epidermis or gastrodermis. In many hydrozoans, these cells differentiate into nematoblasts and subsequently develop mature nematocysts. The distribution of cnidocytes along tentacles and other exposed surfaces underpins effective prey capture and defense.

In humans, cnidarian stings can range from mild irritation to severe pain, depending on species and venom potency.