Did you know that jellies kill more people per year than great white sharks do? Box jellies are the most dangerous of all our slimy friends. Approximately 65 deaths each year are attributed to box jelly stings. If that didn’t catch your attention, I don’t know what will.
Though most Jellies do not carry the reputation that box jellies do, they are fascinating just the same. Take for instance this little morsel of information; did you know that all jellies use the same hole to eat as they do to excrete their waste? Fascinating, and I bet you didn’t see that one coming.
You may be wondering why I keep referring to these gelatinous wonders as "jellies." Well, truth be told, we’ve all become a little bit more politically correct in recent years, I included, and here is a way to lend some respect to our finless friends. Not a fish, or made out of jelly, talk amongst yourselves.
So, all of you self-described marine biology nerds, pull out your prescription facemasks and let’s talk about jellies.
Jellies belong to the phylum Cnidaria. The word Cnidaria is derived from the Greek word "cnidos," which stands for stinging nettle. Although some say this is what Cnidaria stands for, I like to refer to it as, "animals-that-will-give-you-a-rash." Anemones, true corals, sea pens, box jellies, siphonophores, hydroids, fire corals, and true jellies all belong to this phylum. However, upon further classification, we find that true jellies are described in their own class entirely, Scyphozoa. In fact, some of the more conspicuous creatures referred to as jellyfish and not true jellies at all. For example, Portuguese man-of-war belongs to the class Hydrozoa and box jellies belong to the class Cubozoa. So, the next time you have a conversation about jellies, and someone says that their least favorite jelly is a Portuguese man-of-war, you can pull out your marine-biology-second-stage-protector and correct them by saying, "A Portuguese man-of-war is not actually a true jelly, but rather a hydroid that belongs to the class Hydrozoa, whereas true jellies belong to the class Scyphozoa." Stick your chin up high; they will respect you for taking a stand on such important current issues.
So let’s discuss a bit of jelly morphology. These critters possess a very simple body form and make-up. Instead of a brain, true jellies possess a nerve net, which consists of receptors capable of detecting light, odor, and other stimuli. The gelatinous substance for what these aliens of the water world get their name is known as mesoglea or middle jelly. Two layers, the epidermis and the gastrodermis, surround the mesoglea. As their names imply, the epidermis is the outer layer and the gastrodermis is the inner layer that coats the gut. The cavity that serves as both entrance and exit is more appropriately referred to as the coelenteron. The coelenteron is a characteristic shared by all Cnidarians. Blehhh.
The life cycle of true jellies involves two different body forms, which is referred to scientifically as an alternation of generations. The more conspicuous body form is the medusa, the one with which all of us divers are familiar. However, the less evident body form is the polyp. Jellies are either male or female and reproduce sexually (there are some species that contain both male and female organs). When an egg is released into the water column and fertilized, it then plants itself on a rock or other hard surface to develop. This is the polyp life form. As the stalk develops, referred to as a scyphistoma, miniature jellies pop off the end and are released into the water column. These miniature jellies are referred to as ephyra and after a few weeks grow into the medusa form of which we are all so affectionate.
As much as we’d like to think that jellies have one-track minds, "sting the humans," they actually are at the mercy of water currents with little mobility of their own. This mobility is typically vertical and based on the direction and intensity of light from the sun.
Ok, so let’s get to the good stuff, jelly stings. All jellies are equipped with a specialized cell, referred to as a cnidoblast, for defense and feeding. A miniature harpoon-like mechanism is coiled within the cnidoblast and is outfitted with barbs as well as venom. The amount and intensity of venom varies between species, as I think we are all well aware. These nematocysts are concentrated on the tentacles and a single tentacle may contain thousands of them. Triggers of nematocysts are activated when contact is made with another object. Unfortunately, sometimes WE are that object, and not the intended small prey! For anyone out there that is a fan of the TV-show Friends, I will say here and now that peeing on a Jelly sting is not recommended! In fact, the urea may cause the nematocysts that have not yet fired to inject venom. The best treatment for a mild sting is water as hot as you can stand, which will denature the proteins. White vinegar also works well, but is not always on hand when you are in a pickle.
If any of you have been so lucky to visit Jellyfish Lake in Palau, you would know first hand that jellies are not restricted to salt water and can occur in fresh water as well. In fact, a new species of freshwater jelly was described in the United States around 1991. This species, Craspedacusta sowerbii, is still being discovered in new bodies of water throughout the northern states. An eleven-year-old girl, Alex Fegley, is credited with the discovery of this species in Nebraska this past summer.
Jellies occur in a wide variety of sizes, shapes and colors. Most are translucent, occasionally transparent, and even on rare occasions brilliantly colored. Their sizes range from less than an inch to bells at 7 feet across and tentacles over 100 feet long. Regardless of their size, shape or color, jellies are almost entirely made up of water. In fact, 95 percent of their bodies are water. If you’ve ever seen one wash up on shore, you may have seen this first hand as that elegant, fluid creature has been reduced to a gelatinous and sandy pile of goo.
So, the next time you see a jelly while diving, try to steer clear of its tentacles, but do appreciate what fascinating critters they actually are.