As kids most of us learned the common names of many of the plants and animals we encountered in our everyday lives. We learned the common names of various trees, flowers and butterflies as well as names of iconic species such as the bald eagle and killer whale. For many years and most applications our use of common names seemed perfectly sufficient when it came to communicating with our peers. Aside from cartoon aficionados that sometimes referred to the speedy and often mischievous Road Runner as Hot-roddicus supersonicus, most of us didn’t have a clue about the taxonomic names used by members of the scientific community.

Then along came high school. I think its reasonable to believe that many divers remember at least some of the basic tenets concerning the classification of living organisms and their ancestors that were presented in our high school biology classes. I suspect you remember that plants and animals are given a unique taxonomic name that includes a genus and species. In many instances these names are the sometimes strange, often ridiculously long, almost impossible to confidently pronounce Latin and Greek words that all of us Homo sapiens had to memorize in school. Over the years, for many people that did not pursue some kind of career that involved biology, the specifics of what we learned about taxonomic names and the way animals are classified slowly faded into the recesses of our minds. 
Then, at least for us, along came diving. During the majority of conversations among divers, the use of common names is perfectly acceptable. But even though that is the case, it usually doesn’t take too long before someone uses a taxonomic name or term in an effort to avoid confusion and be precise even when we are just sitting around shooting the breeze between dives and at social gatherings. Terms with a seemingly scientific bent such as pinniped, cetacean, echinoderm, cnidarian and Carcharodon carcharias (great white shark) are often used in casual conversations between divers. 
Sometimes it can be a little intimidating to be in the presence of other laymen that appear to know the meaning of all of those words and terms when their meanings are a little fuzzy in your mind. The truth is, the majority of sport divers have varying degrees of understanding and comfort with taxonomy and taxonomic terms. Most of us are learning as we go. This article serves as a refresher on the fundamentals of taxonomy that will help you build your knowledge base and maximize the pleasure you receive from exploring the underwater world.
Why Use Taxonomic Names
Simply put, taxonomy is the science of naming living things. The use of scientific names, more properly called taxonomic names, is a fundamental building block of a practical, yet very precise system for understanding and communicating about the organisms that share our planet. The use of taxonomic names and a standardized system of organization and naming are essential within the scientific community, where exact distinctions among species are necessary. 
Nevertheless, you might question why a non-scientist should bother with all of the Latin and Greek words, and a system of organization that seems to have little to do with our daily lives, instead of just relying upon common names. Interestingly, the primary reason that many laymen use taxonomic names is the exact same reason that scientific specialists do, to be precise and avoid confusion.
Due to the haphazard and highly regional manner in which common names are acquired, it is quite common for the same species to be known by several common names. Take the rather common California fish known as the black-eyed goby, black-eye goby and nickel-eyed goby as an example. Or is that three examples? Further complicating the use of common names is the fact that the same common name is often used to describe different species. As an example, the name “red crab” refers to several species of crabs found in locations around the globe. Given this scenario it is easy to imagine an exchange in which two people believe they are discussing the same animal when they are not. Because one version of a red crab is also known as a pelagic red crab, tuna crab and squat lobster, it is also possible to easily foresee a conversation in which four people are discussing the same species but do not believe that to be the case. 
And there you have it. Common names can lead to ambiguity and confusion.
In the case of red crabs one species is found in central California reef communities and is highly valued as a food source while the other is much smaller, of no commercial value, and only occasionally seen near shore. The advantage to being able to distinguish between these two species is obvious. The good news is that the distinction between these two species can easily be made by using taxonomic names. The taxonomic name of the commercially valuable crab is Cancer productus, while the other is named Pleuroncodes planipes.
Within the taxonomic system, organisms are grouped and named according to their similarities to other species. As a result, certain generalizations can be inferred about a given species just by knowing something about the taxonomic groups in which the animal is described. For example, if you recognize an animal as a sea star, you can infer that it is likely to be carnivorous as is the case with the majority of sea stars. If you know that sea stars are described in the taxonomic phylum Echinodermata, you can also infer that it is likely to be capable of regenerating lost body parts, as is the case with most other echinoderms. Clearly, there are benefits to knowing and using taxonomic terminology. 
Taxonomic Basics
In order to study the world’s creatures and to determine how various species are related to each other, specialists group these organisms into various categories based on commonly shared traits. They have done so with close to two million animals that have been sufficiently described by members of the scientific community. This organizational system is known as taxonomic classification. Introduced by the Swedish scientist Carolus Linnaeus in the late 1750s, the taxonomic system remains the accepted worldwide scientific standard, although the specifics of the system are constantly being debated and revised.
Within the taxonomic system the broadest taxonomic category is that of kingdoms. Back in the 1960s, when I went to high school, taxonomists recognized two kingdoms, the kingdom of plants and the kingdom of animals. However, since that time specialists have recognized three more kingdoms. They are the kingdoms of fungi, protista, and monera (bacteria and cyanobacteria). The reason for including this comment is that, being types of brown algae, kelps are actually types of protists, not plants. While it sounds far sexier to say that giant kelp, Macrocystis pyrifera, is the oceans’ fastest growing plant, the reality is that giant kelp and all other brown seaweeds are protists.
All animals are described in the kingdom Animalia. Within this kingdom there are more than 35 phyla (the exact number continues to be debated). The various phyla are subdivided into classes, which in turn are subdivided into orders, the orders into families, the families into genera, and finally the genera are subdivided into individual species. In some instances the just named categories are subdivided into additional subcategories such as subclass and suborder, but those divisions are beyond the needs of most divers and other laymen.
Species compose the smallest classification group, and every species is unique. Members of the same species are nearly, but not absolutely, identical. For example, all copper rockfish are described as members of the same species, Sebastes caurinus. Treefish are closely related and similar enough to copper rockfish to be classified in the same genus (Sebastes), but they are different enough to be classified as a separate species (serriceps).
Like your own first and last names, which describe both the exclusive group you belong to, your family, and exactly which member of that family you are, your first name, a taxonomic name unambiguously describes where an animal falls within the larger taxonomic scheme. The taxonomic name of a given animal consists of the two most exclusive classification groups “genus and species “and both words are properly written in italics. The first letter of the genus name is capitalized and the entire species name is written in lowercase. This might seem a little confusing when you first read it, but you are probably very familiar with your own taxonomic name, Homo sapiens. 
The table that accompanies this article shows the taxonomic classification of three species commonly referred to as the California spiny lobster, garibaldi, and California sea lion. It should be easy to see from the information in the table that the garibaldi and California sea lion are more closely related to each other than they are to the California spiny lobster. All three are described in the kingdom Animalia, but the lobster belongs to a different phylum than the garibaldi and the sea lion. Garibaldi and California sea lions, along with all other animals that have backbones, are grouped together in the phylum Chordata. Lacking a backbone, spiny lobsters are invertebrates classified in the phylum Arthropoda, one of the many phyla that describe invertebrate animals. 
You can also deduce that California gray whales, types of vertebrates, must also be more closely related to California sea lions and garibaldi than they are to California spiny lobsters. Similarly, sheep crabs, types of arthropods, are more closely related to California spiny lobsters than they are to garibaldi and sea lions.
As divers we are often satisfied just by knowing more or less where an animal fits into Mother Nature’s overall scheme. But whether vertebrate or invertebrate, big or small, the more you know about an animal’s traits, who an animal is related to and how it is classified in the larger taxonomic scheme, the more you can infer about its role in the marine world. 
Hierarchy of Taxonomic Classification