Stalking
the lingering sting
WW sheds light on mysteries of marine organisms
By Callan Bentley
Flat Hat Variety Editor
Late one evening last fall, some other nature-loving Flat Hatters and I went to a small beach on the shore of the James River, just off the Colonial Parkway. The moon was low, and we noticed what looked like small sparkles of moonlight being reflected off the small waves. But the little flashes of light seemed to last just a little bit too long, and so we investigated further.
As it turned out, it wasn't moonlight that was making the waves light up. Thousands of small luminescent jellyfish filled the water. When stimulated (disturbed by a wave's action or by a hand swept through the water) an X-shaped area on the jellyfish's top side would luminesce to a soft blue-green.
Luckily, the little glowing creatures did not sting us while we ran our arms through their multitudes. They were as big as quarters and nickels, although a few reached up into the half-dollar range.
This is approximately the size of the most common Atlantic jellyfish, Gonionemus murbachii. The largest jellyfish on the planet, Cyanea artica, can measure up to an incredible eight feet in diameter, with tentacles trailing 200 feet below it.
No one knows what it is like to be stung by one of these eight-foot monsters though, as they live in waters so cold that a swimming human would not last more than half a minute in them. One can imagine it would be painful, however, as other jellyfish in the same Cyanea genus (but only a foot across) show up in temperate Atlantic waters every summer and deal out a ration of angry red welts. The stings can be more than just painful: if the toxin strongly affects your body, you may succumb to muscular cramps. If you're in the water when this happens, drowning is likely, and you had better hope the lifeguard is looking your way.
Jellyfish are filed taxonomically in the class Scyphozoa, under the phylum Cnidaria (the "C" is silent). Sometimes referred to as "the flowers of the sea," their fellow cnidarians include anemones, corals, and hydra (those little transparent palm-tree-looking things you might have looked at under a microscope in high school biology lab). This may seem like a bit of an eclectic list, but it makes more sense when you realize that there are two stages in the cnidarian life cycle. All go through a medusa stage at some point (the jellyfish that we recognize spends most of its life in this form) and a polyp stage (which is exemplified by a hydra or an anemone). Though the polyp is sessile and the medusa is mobile and free, one is essentially an upside-down version of the other.
Of the 9,000 species of coelenterates, most are marine species. A scant few do venture into the freshwater realm: hydras, for instance, as well as a species of hydroid that parasitizes sturgeon eggs, and two small jellyfish.
When people think of jellyfish, they tend to focus on the animal's ability to sting. All cnidarians have cells in their skin called nematocysts which discharge hollow threads when stimulated. Sometimes these hollow threads will be sticky and adhere to their prey, sometimes they will wrap around it like a lasso, and sometimes they will penetrate it and inject a toxin. The nematocysts are located in the tentacles that hang in a circle below the swimming jellyfish.
The ring of tentacles outlines the edge of the jellyfish. Their bodies are circular, what is referred to as a radially symmetric body form. This means that they're built along the same lines as a pizza pie. Humans, on the other hand, are more like a submarine sandwich, with a distinct left and right side. Jellyfish lack any sense of left or right; all they distinguish is up from down.
Their mouth is located in the center of their body, bottom side. Any food caught in the tentacles is shoved into the mouth. Once inside, digestive juices turn the food into a thick broth. The broth then circulates about the body, with hungry cells absorbing the nutrients they need.
The mouth also serves as the jellyfish's anus - it is the one and only opening into the digestive system.
Not only is the jellyfish's digestive system primitive, but the animal's nervous system is too. Jellyfish altogether lack brains and any semblance of a central nervous system. The phrase "spineless as a jellyfish" derives from this fact, I suppose. Instead they have a neural net - a weblike arrangement of nerves that conveys information from one area of the body directly to all the others. It is as if jellyfish are alive when no semblance of awareness. All their actions are instinctual; they move without a sense of where they are headed or what they are escaping from.
While jellyfish may seem
crude and primitive to us, it is worth considering that evolutionarily speaking,
they are a successful species. Jellyfish showed up far back in geologic time,
at the close of the Proterozoic. In other words, when multicellular life was
just getting started, jellyfish took the stage, and they've been there ever
since. By comparison, humans have but a brief cameo role. Jellyfish persist
today because their crude body forms and lifestyles have done them a world of
good.