Thomas Meadows, ago 11, of Peoria, Illinois, for his question:
What is the life cycle of a jellyfish?
Stranded on a shore, a jellyfish is a sorry sight, a blob of pale gristle and tangled threads. But moving through his watery home he is as graceful as a floating parachute. His family name is Medusa, borrowed from a legendary lady of ancient Greece. This lady was said to be a horror with snakes instead of tresses. Anyone who saw her was turned to stone ‑ or so the old legend says.
The jellyfish Medusa is a parachute with trailing tresses. The tresses are tentacles equipped with stingers. Many a swimmer has been stung when he tangled with the streamers of a jellyfish. As far as humans are concerned the worst of them all is the blue beauty called Portuguese man-of‑war, though even he cannot turn a person to stone. However, a jellyfish’s stingers can paralyze a smaller fish on which he intends to dine. The victim is quite helpless and maybe feels as if he has been turned to stone.
About a thousand different jellyfish make their homes in the sea and a few live in fresh water. The giants measure more than two feet over the parachute and trail 20 or 30 foot streamers. The midgets of the family measure four or five to the inch. The parachute may be a gas filled balloon, a gob of watery jelly or a lump of quite solid gristle. The colors may be blue, pink, brown or glassy white.
In most cases, growing up is a very complicated business for a jellyfish. A new generation begins when Mamma lays a fertilized egg called a planula. This rather flat oval planula has little hairs which it uses to swim freely through the water. Finally it finds a solid rock and settles. It grows into a polyp, which is a blob of gristle with tentacles. The little fellow is now in the hydra stage. All summer long it feeds and grows, sprouting other polyps. Come winter, the tentacles vanish and the hydra stretches until he becomes a longish rod.
He is now in what is called his strobila stage, a series of round grooves appear in his long body. He begins to look like a concertina. The grooves deepen, the raised rings grow frilly edges. Is this a pile of midget doilies? Into it is a pile of little unborn jellyfishes.
Day by day the strobila looks more and more like a pile of fairy saucers. They seem to be separating, especially the ones near the top. And so they are, One day, the little fellow at the top pulls himself free. He is a baby jellyfish, a tiny round blob with a frilly edge. This brand now jellyfish is called the ep:nysa.. Off he goes in the water. He is ready to swim about, feed and grow until he looks just like his parents.
The Portuguese man‑of‑guar is actually a colony of little polyps sharing a floating gas filled balloon. The colony moves when the wind blows the balloon. Most jellyfish have muscles to open and shut their parachutes, This enables them to swim about as they choose. They can even move up and down in the water.
In most cases, the jellyfish has fragile muscles at the edges of his parachute, when open, the chute fills with water. As it closes, the jet of released water forces the jellyfish in the opposite direction. He moves along in jerks, trailing his graceful streamers far below him.