Edward Wingate, age 12, of Florence, South Carolina, for his question:
Can a jellyfish be classed as a real fish?
To qualify as a genuine fish, an animal must have a backbone and nature attaches a backbone to a complete skeleton on internal bones. A jellyfish, of course, is a spineless animal with not one reliable bone in his wobbly body. Zoologists classify the animal kingdom on basic biological features of this sort. The ownership of a backbone is so important that it is used to divide all the animals into two major categories. Backboned animals, including the fishes, are vertebrates. Animals without backbones, including the jellyfishes, are invertebrates.
Many so called fishes of the sea are not really true fishes. The list includes starfish and shellfish and also the jellyfish. They are not related to fishes and many are not even related to each other. The orderly classification of the animal kingdom reveals who is related to whom and exactly why. The keys to this system are basic biological features. The million or so species of animals are sorted into several large phyla, or tribal groups. The members of each phylum share a few common features. Those that share more and still more basic features are sorted into smaller and still smaller groups.
The names of many groups are strange tongue twisters. They are scientific terms with hidden meaning that give clues to biological features. For example, a backbone is made of vertebrae. A backboned fish is a vertebrate, where as a spineless jellyfish in an invertebrate. Phylum Protozoa, meaning first life, includes the one celled animals, similar to the earth’s first creatures. Phylum Porifera, the pore bearers, includes the pore riddled sponges. The jellyfishes have a more advanced feature which places them in Phylum, Coelenterata meaning hollow stomach.
True, many other animals also have hollow tummies, especially before dinner.
But a coelenterate body is a bag of jelly or gristle around a very special hollow stomach that has one opening to let water flow in and flow out. There may be tentacles to swish the two way water traffic that brings in food and oxygen and washes out wastes. This basic body structure is shared by about 9,000 assorted coelenterate animals. The phylum includes the charming sea anemones, the somersaulting hydras and all the jellyfishes. Other features are used to sort the coelentrates into separate classes.
Most of the 200 or so jellyfishes belong in Class Scyphozoa, meaning cup shaped. The magnificent Portuguese man of war jellyfish belongs with the hydra in Class Hydrozoa. This class was named for a many headed monster of ancient legend. Class Ctenophora, the comb bearers, includes jellyfishes that have rows of soft plates.
Most jellyfish are fist sized animals, found floating on or near the surface of the sea. They have jellified umbrellas that open and close to give them a limited mobility. Their trailing tentacles entrap food, which includes smallish plants or animals, alive or dead. The tentacles of some jellyfish are equipped with very painful stingers.