Sting

 "No sweet perfume ever tortured me more than this"
- "Desert Rose" by Sting

Have you ever been stung by a jellyfish? Or touched the tentacle of an anemone? Some of them hurt; some don't. All cnidarians (jellies, anemones, and their relatives) have stinging cells in their tentacles called cnidocytes. Since I've been working on a paper about a cnidarian recently - the hydroid Bouillonia cornucopia - we're going to take a time-out and talk about cnidocytes.

Cnidocysts in Bouillonia cornucopia.
Photo by Caitlin Plowman.

First of all, they're super cool. The "sting" you feel is actually a little mechanical barb piercing your skin. In some species, like intertidal green anemones on the west coast of North America (Anthopleura xanthogrammica), the barbs aren't strong enough to actually penetrate your skin, so it just feels sticky. Cnidarians use their barbs to capture prey and defend themselves against predators. A mechanical stimulus changes the water pressure in the cell and triggers the barb to shoot out.

In Bouillonia cornucopia, the cnidocysts have kind of a coffee bean shape. My collaborator, Caitlin, found them in a histological section she made from some specimens I sent her from the Arctic deep sea. Check out this image at right. This is a cross-section through a B. cornucopia tentacle. The cnidocytes (stinging cells) form a ring around the outside. I've pointed out a few of the cnidocysts (barbs) with white arrows. There they are, poised and ready to shoot out if anything dare touch them. 

Cnidocytes in Bouillonia cornucopia tentacles. Photo by
Caitlin Plowman.

Cnidarians are pretty simple organisms compared to other animal phyla, so it's cool for me to think about is how cnidocytes help them survive. Using these mechanically-triggered stinging cells means that many cnidarians are tactile predators - they hunt by touch, rather than by sight. This gives jellies a significant advantage over fish as predators in murky waters and helps cnidarians feed in other environments too. In the Arctic deep sea, it's completely dark, so cnidarians like B. cornucopia use their stinging cells to capture small particles and organisms from the water column to feed. 

I was excited to see the cnidocytes in my B. cornucopia specimens - they were a neat find!