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Biology LibreTexts

1.5: Scientific Nomenclature

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  • Scientific nomenclature is based on a taxonomic classification system. Taxonomic classification is a hierarchical system used to classify and compare organisms. There are 8 ranks in this system, listed below in the order of the most general (broadest) to the most specific:

    1. Domain

    2. Kingdom

    3. Phylum

    4. Class

    5. Order

    6. Family

    7. Genus

    8. Species

    Prokaryotic organisms like bacteria may have classifications below the species level, including strain, subspecies, serotype, morphotype or variety. Taxonomic classification indicates how closely organisms are related. For example, two organisms sharing the same Class are more closely related than two organisms sharing the same Phylum.

    Binomial nomenclature: The scientific name of an organism consists of two words: the genus name and the specific epithet. The genus name comes first and is always capitalized; once identified it can be abbreviated to a single letter. The second word is known as the specific epithet and is not capitalized. The two words together make up the scientific name or species name. The genus can be used alone (you can refer to the genus Staphylococcus or the genus Bacillus) but the specific epithet without the genus name has no scientific significance. Scientific names in print should always be either italicized or underlined and should always be underlined when written. For example, the scientific name for human beings is Homo sapiens or H. sapiens. The scientific name of a bacterium is Staphylococcus aureus or S. aureus.

    The scientific name often includes a description of the characteristics of an organism. The scientific name Staphylococcus aureus tells you the morphology and arrangement of the individual cells belonging to this bacterial genus (staphylococcus = spheres in clusters) and also tells you that S. aureus often grows in colonies with a golden color (“aureus”). Although scientific names are often descriptive occasionally these descriptions can be deceiving. For example, Haemophilus influenza is a bacterium (not a virus), and does not cause influenza.