Eva Miller, age 11, of Englewood, Florida, for her question:
What does a jellyfish eat?
The numerous different jellyfishes range in size from thimbles to big patio umbrellas. Some of the little ones live in fresh water. But most species drift through the salty, sunlit seas. All of them are hunting for food and most of them feed on meaty seafood. A few feed on plankton, a mixed diet of mini plants and animals. And all the jellyfish are armed with stingers to stun their prey. So let's beware.
The average jellyfish looks somewhat like a pretty plastic umbrella, dangling ribbons of trailing tentacles. Usually his glassy dome, or cup, is tinted with flowery shades of blue and pink and purple and often topped with a dark stenciled design. The colorful creature pulses along through his blue green watery world by opening and closing his umbrella. He opens to capture a scoop of water and closes to jet it out behind him and the force of his little jet stream pushes him forward.
He may be one animal or a colony of small polyp creatures, sharing one same um¬brella. In any case, those dangling tentacles are trawling for food. The preferred diet includes shrimps, smallish fishes and a wide assortment of sea worms. Victims trapped in the tentacle net are paralyzed by nasty little stingers.
The mouth of the average jellyfish dangles down on a tube, which may be quite short or quite long. The food is transferred to the digestive system, which is located on the underside of the cup and a system of small channels distributes the nutrients throughout the entire body. This system is helped along by armies of small hairs that wave streams of water in and out.
The remarkable body is a model of simplicity. It is enfolded in roundish bag, which is made of a sort of jelly sandwich. Actually the outer covering is made from two layers of living cells and between them is a thick layer of jellified substance, which is why the jellyfish seems to be made of jelly.
He has a few simple nerves and several simplified sense organs. But he has no teeth and no other method to chew his food. All his nourishment must be served in liquid form. Some of the multiple jellyfish do this with special tentacles that end in dangling lips.
When a smallish fish is trapped below, these mobile lips surround him on every side. First they pour in digestive juices and dissolve the solid fish food. Then the liquid formula is sucked up into the jellyfish's body.
Some jellyfishes are too small to cope with shrimps and such. They live where the waters are rich with plankton and feed on an assortment of single celled animals and algae. All the medium and large jellyfishes are carnivorous meat eaters. But the plankton eaters settle for a mixed seafood salad of mini vegetables and microscopic bits of meat.