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The Journey of Mr. Sand Dollar: Systematics 101

A scientist who searches for, describes, and classifies species (some of which might be new to science) is known as a systematist. Systematic studies (the discipline of systematics) are the first steps towards understanding the evolutionary relationships among different species and how all the extraordinary biodiversity of our planet fits together. In this article, we take a closer look into the world of systematics. To do this, let’s revisit the fantastic journey of Mr. Sand Dollar that was outlined in the video on studying biodiversity in the lab.
After being collected from the shallow seas of the Philippines by scientist Dr. Rich Mooi (he’s the talent behind the sketching and narration in the videos!), Mr. Sand Dollar has come to rest on one of the innumerable shelves of the California Academy of Sciences’ specimen collections. In addition to ensuring that Mr. Sand Dollar is properly preserved so that his body remains intact, all the data that were collected about Mr. Sand Dollar during the expedition are carefully stored in the computerized database under Mr. Sand Dollar’s unique catalog number. Mr. Sand Dollar is now officially a specimen in the collections.
But the systematist’s work is not done just because Mr. Sand Dollar has a catalog number – there’s lots more to do! The first task is to record Mr. Sand Dollar’s gross morphology. This means that the systematist will spend many hours in the lab, observing the specimen under a stereo microscope, measuring and making detailed sketches of every part of the animal’s body. Recording the fine details of a specimen is one of the fundamental skills of a systematist, because that information will be used to decide whether Mr. Sand Dollar represents a new species. While observing the morphology of the specimen, our systematist notices two posterior (toward the a rear) holes in the body of Mr. Sand Dollar. The shape and size of these holes can be important features of a sand dollar, helping to narrow down the main sand dollar group to which it belongs. Combined with other features, the systematist can begin to see that this is shaping up to be a pretty exciting specimen.
Next, the systematist searches through the scientific literature for species descriptions that might match that of Mr. Sand Dollar. After searching thoroughly for any mention of Mr. Sand Dollar’s unique morphological features and not finding anything that is a clear match, the systematist decides that more information is needed. It’s time to do some DNA analysis! Fortunately, Mr. Sand Dollar was preserved in such a way that a piece of his tissue can be used to run genetic analyses. Special methods of preserving specimens must be used if molecular work is going to be done at a later time. By sequencing Mr. Sand Dollar’s DNA, the specimen can be compared genetically to other described species of sand dollars from that area of the Philippines or elsewhere in the world.
The DNA results are in, and they support the hypothesis that Mr. Sand Dollar is indeed unique! As big as a molecule of DNA is, it has only four bases: adenine, guanine, cytosine, and thymine. What distinguishes the DNA of one species from that of another species is the particular pattern or sequence of how those four bases are arranged along the length of the DNA molecule. As it turns out, the pattern for Mr. Sand Dollar is slightly different than any other known sand dollar species’ genetic sequence.  This provides more evidence that Mr. Sand Dollar could be a species new to science. Very exciting! With no other references that match Mr. Sand Dollar, the systematist can describe and name the new species and publish the results.
The systemetist also wants to know how Mr. Sand Dollar is related to all the other species of sand dollars that have been described, not just ones from the Philippines. In addition to giving Mr. Sand Dollar his scientific or binomial name, it is also important to determine his evolutionary relationship to other species of sand dollars. Connecting species by their hypothesized evolutionary relationships is the study of phylogenetics. By combining many forms of evidence, like the gross morphology and the data from genetic sequencing, an evolutionary tree can be hypothesized that illustrates Mr. Sand Dollar’s relationships to other sand dollars.
In the published paper that describes Mr. Sand Dollar as a new species, and gives him his scientific name, he is designated as a holotype, the specimen that uniquely bears the name for the species to which he belongs. Other specimens of the same type of sand dollar that were collected on the expedition can be designated as paratypes. However, only the holotype "officially" bears the name of the new species. It's a bit as if Elvis Presley himself showed up at an Elvis impersonation convention. He would be sort of like the holotype. All the other "Elvises" might look an awful lot like the real Elvis, but only one legally bears the name "Elvis Presley."
The formal description of the holotype and paratypes is published in scientific journals so that other scientists who study sand dollars can review and possibly debate Mr. Sand Dollar's proposed classification as a new species and can use the information to inform their own research. This process of discourse is a very important part of the scientific process.
Of course, this formal description of Mr. Sand Dollar will include a proper scientific name! Every species that systematists have ever described has a unique scientific name. The scientist who describes the new species gets to decide the species’ name, and it can be almost anything…as long as it is a “Latinized” word selected according to the rules of nomenclature. These rules are regularly reviewed by a committee of systematists that is responsible for maintaining and updating the rules. Scientific names frequently describe what the organism looks like, or where it was found.  Sometimes, the species is named in honor of someone -- but the describer cannot name it after him or herself! That’s part of the scientific naming process, known as binomial nomenclature. This naming system was developed by the Swedish scientist Linnaeus in the 18th century. The process by which names are selected, and arranged in groups so that organisms can be placed together according to relationships to each other is called taxonomy. Taxonomy constitutes a sort of filing system for all the names that are developed through the process of systematics.
Having a standardized system of naming species is crucial for systematics, and science in general, because it allows scientists around the world to communicate easily and reliably about the organisms they are collecting and studying. We have fondly referred to this particular specimen as Mr. Sand Dollar, but our systematist would be sure to use the scientific name when he sends a picture of the specimen to his colleague in Austria who is also studying sand dollars. Such is the journey from living organism, to valuable holotype specimen, to a newly described species of sand dollar!

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