November 3rd is Jellyfish Day! Despite their common name, these animals are not fish at all, and are more accurately called “jellies”, although you wouldn’t want to spread them on your toast! Jellyfish are soft-bodied invertebrates, meaning that they have no skeleton, unlike true fish. Their body is made up of a gelatinous “bell”, with tentacles that dangle below. These tentacles deliver a toxic substance when they come into contact with another organism, which helps the jellyfish to capture its prey. When the tentacles touch a human being, they can deliver a painful sting. Jellyfish tentacles also protect against predators, although some creatures, such as certain sea turtles, find them to be a delicious treat!
The term jellyfish usually applies to the classes known as Scyphozoa (“true jellyfish”), Cubozoa (“box jellyfish”) and Staurozoa (“stalked jellyfish”). These creatures have roamed the world’s oceans for hundreds of millions of years, and though a few hundred species are currently recognized, there are likely many more waiting to be discovered. Jellyfish come in many striking different colors and sizes. Some are less than an inch long, while the largest, known as the Lion’s Mane Jellyfish, can be over six feet across with tentacles more than one hundred feet long!
Most of us think of jellyfish as the tentacled creatures floating through the sea, but this is actually only one stage of their life cycle. After hatching, the small jellyfish larvae search for a nice spot to latch onto. It then moves into its “polyp” phase, attached to a single location on the sea floor. Eventually, when the conditions are right, it becomes a “medusa”, a free-swimming organism that will grow into the jellyfish that most of us are familiar with.
Jellyfish stings, while painful, are not especially dangerous to humans for the most part. Some box jellyfish species found in the Cubozoa class, however, can be deadly. Stings are usually treated with vinegar, but more severe stings may require quick medical attention. While it is a common belief that pain from a sting can be lessened by peeing on it, this can actually make the situation worse by causing the cells embedded in the skin to release more venom. Interestingly, even a very thin body covering such as panty hose has been shown to resist jellyfish stings, as the tentacles only release venom when they detect certain chemicals in skin.
Jellyfish can be quite beautiful, when viewed safely and from a distance, and are quite fascinating animals. However, be sure to exercise care and caution when entering any water where jellyfish are known to swim.
Bernie’s Bonus Fun Fact: One species of jellyfish can replenish its cells through a process called “transdifferentiation”. This means the jellyfish is actually “biologically immortal” meaning it does not grow older and become weaker with age like most organisms, and won’t die unless it succumbs to injury or illness.