Cnidarians: Stinging Nettles of the Animal Kind

“Ouch, something just stung me.” This is a common phrase to hear someone say (I’ve heard myself say it) while enjoying the otherwise soothing waters along our beautiful Gulf Coast. We host an amazing variety of marine organisms that possess the ability to sting when contacted. I’m referring to organisms in the phylum Cnidaria (pronounced “ni-dair-ee-ah”), which includes about 10,000 species that have been identified. There is general agreement on the classification of five different classes of cnidarians, all of which have stinging cells, but most of which are not dangerous to humans. These include Class Anthozoa (anemones and corals), Class Cubozoa (box jellyfish), Class Scyphozoa (true jellyfish), Class Staurozoa (stalked jellyfish) and Class Hydrozoa (hydroids i.e. Portuguese man o’ war). I’m always intrigued by the origin of scientific names so here is a slight tangent for you on the group names (Cnides: from the greek meaning nettle)(Antho: flower-like; Cubo: cube-shaped; Scypho: cup-shaped; Hydros: sea serpent; Stauro: cross-shaped). The term “zoa,” of course, refers to animals.

Most of the time you are stung in our local waters it involves the classes Hydrozoa or Scyphozoa. The Hydrozoans are a complex group of organisms but most species go through two distinct stages during their life cycle. The hydroid stage takes the form of a polyp which is composed of a stalk and tentacles at the end. Polyps can be single but are often colonial, connected by tube-like structures. Most polyps are specialized for feeding but others are used to reproduce. Reproductive polyps lack tentacles but have many buds which form the medusa stage of the organism for reproduction purposes. Medusae of the hydroids are similar in design but typically smaller than the medusae of the true jellyfish. Some hydroids also have specialized defensive polyps with numerous stinging cells and one species even has a specialized polyp that develops into a large balloon-like float that the others attach to (the man o’ war). There is one specific type of hydroid in our area that closely resembles a piece of branching brown algae, such as Sargassum. The polyps are scattered along the branches and when brushed against they fire their nematocysts (stinging cells) producing a painful sting. The burning sensation can last for several minutes and you would have sworn the only thing around you was a harmless piece of drift algae.

The true jellyfish, of Class Scyphozoa, also go through a polyp and medusa stage. The polyps of this class are typically single and settle to the bottom as larvae and attach themselves. Over time the polyps mature and produce other polyps by budding, or bud medusae off their upper surface. These jellyfish medusae are microscopic at this stage and many take years to reach maturity, complete with a cup-shaped (scypho= cup shaped) bell and tentacles hanging beneath.
The subsequent lives of these translucent marine creatures is no less intriguing than the processes involved in their development. Check out this website from the Smithsonian for more great information.  The next time you feel the burn of a host of nematocysts injecting you with their potent venom, I dare you to stop for just a second to be amazed by the fascinating creature that you have just met. If you can pull this off you are well on your way to becoming the quintessential nature nut!  Click here for helpful information if you are stung.