The New Student's Reference Work/Animal Kingdom
Animal Kingdom. the name applied to the group containing all animals, separating them from the vegetable and mineral kingdom, respectively. It is a very old arrangement to divide all nature into three kingdoms—animal, vegetable and mineral. Cuvier named one of his most famous books, the Animal Kingdom (Règne Animal), and in it divided animals into four divisions, based on their plan of construction, as follows: vertebrata, the backboned animals; mollusca, the soft-bodied animals, such as snails, clams, etc.; articulata, all jointed animals, thus including lobsters and crayfishes with the worms; radiata, animals like the starfishes, sea anemones, etc., having a radial arrangement of parts. These divisions have long been out of use, for the reason that they do not represent the real state of the case. The animal kingdom is now divided into a larger number of branches, called sub-kingdoms. While there is a tendency to increase the number, the following eight sub-kingdoms represent a modern arrangement, 1. Protozoa, the simplest animals, microscopic and single celled. All animals above the protozoa art many-celled, and are spoken of collectively as metazoa. 2. Porifera, the sponges. 3. Cœlenterata—the jellyfishes, hydroids, sea anemones, coral animals, etc. 4. Vermes, the worms, a very large and complex group, including the jointed worms, leeches, earth worms, the smooth worms, the shelled worms, like brachiopod shells, etc. 5. Echinodermata, animals with spiny skins, like starfishes, sea urchins, sea cucumbers, etc. 6. Arthropoda, the articulated animals, with jointed limbs—spiders, insects, myriapods, crustacea. 7. Mollusca—snails, oysters, clams, cuttlefish, etc. 8. Vertebrata: this group includes some of the animals formerly classed with the worms and mollusca. The majority of them have a backbone composed of vertebrae, but not all of them. The sub-kingdoms are coordinate divisions; in other words, equivalent groups. They are further divided into Classes, the classes into Orders, the orders into Families and smaller divisions. On account of the importance of the Vertebrata, the five Classes are named: Fishes, Amphibia, Reptiles, Birds and Mammals. See the different sub-kingdoms under their respective headings.