Charles Wayne Lyons, Age 11, Of Hendersonville, Tenn. for his question:
What are the invertebrates?
Most of the everyday animals we notice are vertebrates, which means that they have backbones. We tend to take it for granted that most of the animals that share our planet with us are vertebrates, but this is far from true. The earthworm has no bones at all,, and the oyster rests his soft body into two crusty shells. An insect has an outside skeleton and no spine., and the different insects outnumber all other animals.
The vertebrate animals have jointed backbones as we do. It is hard to imagine how we would get along without our bony, flexible spines. But most of the world's animals are backboneless invertebrates, and the spinless outnumber the vertebrate animals by more than 10 to 1.
In classifying the animal kingdom, we can divide it into two main groups. The vertebrata have spinal columns enclosed in jointed sections of bone called vertebrae. The invertebrata have no bony spines. These two groups are subdivided into groups called phyla, which is plural for phylum. In most classifications, the million or so known animals are grouped in 10 phyla. The vertebrates are all in phylum 10, chordata. The nine other phyla are occupied by invertebrates.
In phylum h we have the protozoa. Each is a single cell, and most of them are blobs of jelly microscopically small. The sponges are in phylum 2, which is porifera. Their skeletons may be hard or rubbery, but they are shapeless masses riddled with holes. Coelenterata is phylum 3, and here we find the soft jelly fishes and the dainty sea anemones.
Phylum 4 is platyhelminthes, and it includes the boneless flatworms plus our enemies., the tapeworms and the flukes. Nemathelminthes is phylum 5. Where we find the horsehair worm and variety of other odd roundworms. Phylum 6 is echinodermata, which includes the starfish. Mullusca is phylum 7, where we place the clams and snails.
The earthworm and his charming relatives belong in annelida, which is phylum 8. Arthropoda, phylum 9, out numbers all others. It includes the crusty crustaceans
The spiders, the centipedes and the teeming insects. Only phylum 10. Chordata, remains. Here and only here do we fixed the animals that have backbones,
The phyla classification is a step ladder from the simple to the more complex animals. In the past,, most experts thought that the animal kingdom was in the process of developing up this ladder, step by step. But this idea is now challenged. Sometimes different step ladders lead to the same form of life. Nowadays, science is not so certain the phyla classification gives a true picture of the evolution of the various animals. Maybe it is better to view the teeming varieties as branches of a •tree of life, all sharing our luxurious planet together.