Zoological Systematics & Taxonomy

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1 Name: PRE-LAB This lab is designed to introduce you to the basics of animal classification (systematics) and taxonomy of animals. This is a field that is constantly changing with the discovery of new animals, fossils, scientific techniques and the development of a better understanding of the evolutionary relationships between organisms. Systematics is: _ Taxonomy is: _ How many different animal species currently live on Earth? This is not an easy question to answer. There are many regions of the planet that are not wellexplored for animal life, in particular, the deep ocean. Some animal species are only found in very small areas (eg. less than one square kilometer or less), especially in the tropics. Estimates of the total number of all living species generally range from 10 to 100 million (with most estimates between 10 and 20 million). More than 1.5 million animals have been identified and named with most animals being insects and microscopic life forms. We may never know how many different animals there are because many of them have and will become extinct before being counted and described. Some zoologists estimate that less than 20% of all living animals and less than 1% of animals that existed in the past have been named. The tremendous diversity in life today is not new to our planet. The noted evolutionary biologist Stephen Jay Gould estimated that 99% of all plant and animal species that have existed have already become extinct with most leaving no fossils. Also, realize that humans and other large animals are freakishly rare life forms, since 99% of all known animal species are smaller than bumble bees. Linnaeus and Some History of Classification Biologists use a variety of scientific techniques to classify organisms into different categories. Most of these procedures judge the varying degrees of apparent similarity and difference that they can see from the macroscopic to the microscopic to the molecular level. The assumption is that the greater the degree of similarity, the closer the biological and potentially the evolutionary relationship.

2 Today many scientific techniques are used to determine phylogenetic relationships between organisms and establish taxonomy of an animal including: comparative anatomy or comparative morphology is: comparative embryology is: comparative cytology is: comparative biochemistry is: Before the advent of modern, genetically based evolutionary studies, European and American biology consisted primarily of taxonomy, or classification of organisms into different categories based on their physical characteristics. The leading naturalists of the 18 th and 19 th centuries spent their lives identifying and naming newly discovered plants and animals. However, few of them asked what accounted for the patterns of similarities and differences between the organisms. This basically non-speculative approach is not surprising since most naturalists two centuries ago held the view that plants and animals had been created in their present form and that they have remained unchanged. As a result, it made no sense to ask how organisms have evolved through time. Similarly, for these early taxonomists, it was inconceivable that two animals or plants may have had a common ancestor or that extinct species may have been ancestors of modern ones. One of the most important 18th century naturalists was a Swedish botanist and medical doctor named Carl von Linné ( ). He wrote 180 books mainly describing plant species in extreme detail. Since his published writings were mostly in Latin, he is known to the scientific world today as Carolus Linnaeus, which is the Latinized form he chose for his name. For more biographical information on Linnaeus, review the UC Museum of Paleontology at UC Berkeley website at Although fundamental classification of animals may predate civilization, the questions of how classifications are to be constructed are by no means settled. Linnaeus, in 1735, published Systema Naturae. This marks the beginning of the modern classification of plants and animals. He devised practical techniques for the naming of groups of organisms and their ranking and ordering. He developed the system of binomial nomenclature, which is:

3 While the form of the Linnaean classification system remains substantially the same, the reasoning behind it has undergone considerable change. For Linnaeus and his contemporaries, taxonomy served to demonstrate the unchanging order inherent in the natural world. This static view of nature was overturned in science by the middle of the 19th century by a small number of radical naturalists, most notably Charles Darwin. They provided some of the first conclusive evidence that evolution of life forms has occurred. In addition, Darwin and Wallace proposed natural selection as the mechanism responsible for these changes. Late in his life, Linnaeus also began to have some doubts about species being unchanging. Crossbreeding resulting in new varieties of plants suggested to him that life forms could change somewhat. However, he stopped short of accepting the evolution of one species into another. How Zoologists and Taxonomists Classify Animals On discovering an unknown organism, researchers begin their classification by looking for anatomical features that appear to have the same function as those found on other species. The next step is determining whether or not the similarities are due to an independent evolutionary development or due to descent from a common ancestor. If the latter is the case, then the two species are probably closely related and should be classified into the same or near biological categories. How does one identify an unknown specimen? One way is by direct comparison with specimens in a museum reference collection. However, few biologists have ready access to such collections and if they do the collections are often incomplete. Even with such access, most non-specialists would find this a tedious approach, involving working through thousands of museum specimens. In fact, this is part of the foundation of the field of taxonomy. In order for scientists and museums to organize their collections, a set of standards was necessary to make sense of the incredible diversity of organisms as well as for effective communication between biologists. A practical alternative is to use a taxonomic key which is: You will work with a basic taxonomic key as part of today s lab.

4 Major Taxonomic Divisions of Life Be aware that all taxa except the species and subspecies epithets are capitalized; species and subspecies epithets begin with lowercase letters. Genus, species, and subspecies names are printed in italics or are underlined when written or typed. For a complete scientific name of an animal species, both genus and species must be listed. There are 7 major divisions of life which are listed as: (in order) Animals are classified into phyla (the taxa groups into which kingdoms are divided) based on the basic body plans including the presence of true tissues, type of body symmetry, the presence and type of an internal body cavity (coelom), segmentation, and cephalization. TRUE TISSUES A tissue is a: Generally four basic types of tissues are recognized. 1. Nervous tissue = 2. Muscular tissue = 3. Connective tissue = 4. Epithelial tissue = ANIMAL SYMMETRY 1. RADIAL SYMMETRY is: 2. BILATERAL SYMMETRY is: 3. ASYMMETRICAL SYMMETRY is:

5 EMBRYONIC DEVELOPMENT AND BODY CAVITIES The bilaterally symmetrical animals are further classified based on whether or not they possess a coelom. A coelom is an internal body cavity between the gut and the body wall lined with mesoderm. As the digestive system (gut) forms in animals with a true coelom, it may develop in one of two different ways. This determines if the animal is a protostome or a deuterostome. 1. ACOELOMATE (ACOELOMIC ANIMAL) IS: 2. PSEUDOCOELOMATE (PSEUDOCOELOMIC ANIMAL) IS: 3. EUCOELOMATE (EUCOELOMIC ANIMAL) or COELOMATE IS: Using your textbook and the Internet, determine which label belongs with each animal and write it on the blank. The determination of coelom formation must be made by developmental and internal study of the individual animals. You cannot figure out the answer just by looking at the animals look them up in the textbook or on the Internet. Indicate the type of coelom present in each worm. Nematode worm Flatworm Earthworm/Annelid METAMERISM is: CEPHALIZATION is:

6 Use of a Dichotomous Taxonomic Key Following is a brief exercise in classification that shows you how to use a taxonomic key to "run down" or "key out" the classification of an animal when neither its common nor its scientific name is known. You will be given a handout that is a simple key to the more common phyla and classes of animals and free-living protozoans. The key, for the most part, uses external characters that can be visualized without dissection. It is designed for use with adult specimens. Like most keys, this key is utilitarian in the sense that the animal groups are not arranged in perfect phylogenetic sequence, and the characters used in the key may have no particular phylogenetic significance for the taxon. They are simply the characters that typically provide the best assurance of correct identification. A two-choice system serves as the basis of a dichotomous key. In the dichotomous key, two contrasting alternatives are offered at once, so you can choose the one that fits your specimen. At the end of the choice, you will find a reference number to the next set of alternatives to be considered. Again make a decision and proceed in the same manner until you arrive at the scientific name of the animal or the taxon to which it belongs. This key also has the capacity for reverse use so that you can retrace your steps if you make a mistake. In each couplet, the number in parentheses refers to the number of the couplet from which that couplet was reached. Keep in mind that individual variations exist; keys are based on the average, or "typical," adult specimen, whereas your specimen may be immature or somewhat abnormal. It is often very helpful to examine more than one specimen of a species or group, if available, when a particular descriptive character proves troublesome.

7 CLASSIFICATION PRACTICE Utilize the key to classify the following unknown animals: Indicate phylum or class. PLEASE identify the letter of the specimen you are working with for grading. Also, provide the taxonomic key # sequence used

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