Creature Feature: Peanut Butter and Jellies!
Posted By Abigail Smigel on 22 October 2003
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.
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