Introduction of Zoology
Zoology (Gr. Zoo, animals & logos, to study) is the study of animals. It is one of the broadest fields in all of science because of the immense variety of animals and the complexity of the processes occurring within animals. There are, for example, over 20,000 described species of bony fishes and over 300,000 described (and many more undescribed) species of beetles! Ichthyology, for example, is the study of fishes, and ichthyologists work to understand the structure, function, ecology, and evolution of fishes. Ichthyologists have described a wide variety of feeding habits in cichlids. These fish include algae scrapers, like Eretmodus, that nip algae with chisel-like teeth; insect pickers, like Tanganicodus; and scale eaters, like Perissodus. All cichlids have two pairs of jaws. The mouth jaws are used for scraping or nipping food, and the throat jaws are used for crushing or macerating food before it is swallowed. Many cichlids mouth brood their young. A female takes eggs into her mouth after the eggs are spawned. She then inhales sperm released by the male, and fertilization and development take place within the female’s mouth. Even after the eggs hatch, young are taken back into the mouth of the female if danger threatens. Hundreds of variations in color pattern, body form, and behavior in this family of fishes illustrate the remarkable diversity present in one relatively small branch of the animal kingdom. Zoologists are working around the world to understand and preserve the enormous diversity.
Evolutionary Processes
Organic evolution (L. evolutus, unroll) is change in populations of organisms over time. It is the source of animal diversity, and it explains family relationships within animal groups. Charles Darwin published convincing evidence of evolution in 1859 and proposed a mechanism that could explain evolutionary change. Since that time, biologists have become convinced that evolution occurs. The mechanism proposed by Darwin has been confirmed and now serves as the nucleus of our broader understanding of evolutionary change (chapters 4 and 5). Understanding how the diversity of animal structure and function arose is one of the many challenges faced by zoologists. For example, the cichlid scale eaters of Africa feed on the scales of other cichlids. They approach a prey cichlid from behind and bit a mouthful of scales from the body. The scales are then stacked and crushed by the second set of jaws and sent to the stomach and intestine for protein digestion. Michio Hori of Kyoto University found that there were two body forms within the species Perissodus micolepis. One form had a mouth that was asymmetrically curved to the right and the other form had a mouth that was asymmetrically curved to the left. The asymmetry allowed right-jawed fish to approach and bite scales from the left side of their prey and the left-jawed fish to approach and bite scales from the right side of their prey. Both right- and left-jawed fish have been maintained in the population; otherwise the prey would eventually become wary of being attacked from one side. The variety of color patterns within the species Topheus duboisi has also been explained in an evolutionary context. Different color patterns arose as a result of the isolation of populations among sheltering rock piles separated by expanses of sandy bottom. Breeding is more likely to occur within their isolated populations because fish that venture over the sand are exposed to predators.
Classification of Animals by Scientific Method
Scientific classification in zoology, is a method by which zoologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy. Modern biological classification has its root in the work of Carl Linnaeus, who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent. Molecular phylogenetics, which uses DNA sequences as data, has driven many recent revisions and is likely to continue to do so. Biological classification belongs to the science of zoological systematics. Biological scientists estimate that collectively the earth’s 5 to 40 million species of organisms (depending on the estimate you choose to believe) make up a total of some two trillion tons of living matter, or biomass. The plants comprise well over 90 percent of the biomass. The animals, the focus of this article, comprise only a small percentage of the biomass, but they account for the majority of species.
Modern alternative classification systems generally start with the three-domain system
Archaea (originally Archaebacteria); Bacteria (originally Eubacteria); Eukaryota (including protists, fungi, plants, and animals). In accordance with the Linnaeus method, scientists classify the animals, as they do the plants, on the basis of shared physical characteristics. They place them in a hierarchy of groupings, beginning with the kingdom animalia and proceeding through phyla, classes, orders, families, genera and species. The animal kingdom, similar to the plant kingdom, comprises groups of phyla; a phylum (singular for phyla) includes groups of classes; a class, groups of orders; an order, groups of families; a family, groups of genera; and a genus (singular of genera), groups of species. As established by Linnaeus, the scientists call an animal species, as they do a plant species, by the name of the genus, capitalized, and the species, uncapitalized. The order is: Domain; kingdom; phylum; class; order; family; genus; species. The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens. Homo is the genus, and sapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined. The dominant classification system is called the Linnaean taxonomy. It includes ranks and binomial nomenclature. The classification, taxonomy, and nomenclature of zoological organisms is administered by the International Code of Zoological Nomenclature.
