Animal Classification

The kingdom Animalia consists of three (3) subkingdoms:
     1. Protozoa – one-celled animals;
     2. Parazoa – many-celled animals which do not have a true digestive system; and
     3. Metazoa – many-celled animals with digestive systems.

The Metozoa subkingdom is broken down into 21 divisions, ranging from the very simplest wormlike Mesozoa; to the joint-footed Athropoda (spiders, insects & crustaceans); and Chordata, the animals with simple or true backbones (including fish, reptiles, birds and mammals).

More than 1,250,000 different species, or kinds, of animals have been recorded or described. Many living things still remain to be catalogued. New species of smaller animals, especially insects, are being discovered every year. Throughout the past 300 or so years a system of classification has been evolved known as taxonomy.

English botanist John Ray (1627-1705) was the first person to make an organized classification of living things into species and to group similar species together into larger groups known as genera and families. This classification is usually done by professional biologists in national museums.

The classification scheme used is based on the logical process perfected by Swedish naturalist Carl von Linne (170701778).

A species is defined as a group or population in which the individuals can successfully interbreed. Some groups of animals have many species while others have only a few. There are about 30,000 species of fishes but only 750 species of ribbonworms. The most numerous group is that of the insects, with more than 1,000,000 species.

Each species is given a special scientific name of two parts – the genus and species. It is usually written in italics to show that it is a scientific name. The genus name has a capital letter and the second, descriptive, name has a lower-case letter.

Major groupings of animal classification range from phylum down to species. The system can be illustrated by looking at the full classification of the African lion:
     *Phylum: Chordata
     *Subphylum: Vertebrata
     *Class: Mammalia
     *Order: Carnivora
     *Family: Felidae
     *Genus: Panthera
     *Species: P.Leo

There are about a million or so existing animal species. More than 95 percent of these are invertebrates – animals with no backbone. They include mollusks, arthropods, crustaceans, arachnids and insects.

Animals with backbones, called vertebrates, form only a small fraction of all known creatures. They are generally larger and more mobile. Both size and mobility are made possible by a strong internal bony scaffolding, jointed to give flexibility and held in place by strong connective tissue called ligaments. The eight classes of vertebrates are: hagfish, lampreys & their relatives, cartilaginous fish, bony fish, amphibians, reptiles, birds, and mammals.