The Sting of the Cnidarian (jellyfish and their relatives)


I do a great deal of research when working on my novels and short stories. The as-of-yet untitled novel that I am currently working on involves some genetic manipulation theories, and I needed to learn a little bit more about the anatomy of jellyfish, specifically a type of cell that they have called a cnidocyte. 

The phylum of animals known as Cnidaria, which contains jellyfish, tube-dwelling anemones, minute polyps, and certain types of coral, have a rather unique adaptation that allows the cnidaria to thrive. All of the creatures in this phylum are characterized by cnidocytes, a type of cell unique to these animals. Cnidoctyes function as projectiles, used to ensnare and immobilize prey as well as to defend the cnidarians against those that see them as prey. 

Each cnidocyte is composed of a tough capsule known as a cnida, which stores high concentrations of calcium ions. The cnida is covered by a lid which scientists refer to as an operculum; either a single hinged flap, or three pie-shaped flaps that cover an opening in the cell. A coiled tubule resides inside the capsule until it is triggered by the cnidocil, a hair-like sensory device that is activated by a combination of physical contact and chemical response. When the cell is activated, calcium ions are released into the fluid in the cell, which forces a rapid influx of water causing the coiled tubule inside to spring out- a process that can take as little as seven hundred nanoseconds to complete. Cnidocytes can only be activated once then it takes approximately two days for the cnidarian to grow new stinging cells.

Cnidocytes come in three different classifications. Ptychocysts are used to build protective tubes rather than to catch prey and are unique to tube anemones. Spirocysts are hollow tubules that adhere to the things they come in contact with, entangling their prey, and nematocysts. Nematocysts are the most prevalent of the three, they contain hollow tubules with spikes on the end that penetrate the skin, in most cases injecting the victim with some form of neurotoxin.

Handling Stings

  • Rinse the area with vinegar or warm water (avoid seawater or cool water)
  • Avoid rubbing the area or scraping the stingers off as this can push additional toxins into the wound
  • Pull off any remaining tentacles with tweezers, do not use your hands

Dangerous Symptoms: Call an Ambulance

  • Stings cover a large part of the body, or are located on sensitive areas such as the eyes or mouth
  • Difficulty breathing or swallowing
  • Swollen lips or tongue
  • Nausea or vomiting
  • Muscle spasms
  • Headache
  • Dizziness


The type of neurotoxin and the amount of damage it does can vary greatly between species, as can the overall size of the cnidocyte cell. Sea anemones have cells so small that they don’t penetrate human skin but to certain marine animals such as small fish they are deadly predators. Jellyfish stings are more likely to affect humans, with effects ranging from slight pain accompanied by redness, itching, or numbness at the site to cardiac arrest, depending on the species and amount of toxin injected.