From the Archives: Shrimp Tails - Describing a New Species

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

***Just wanted to thank everyone for the support while my son was ill. It meant so much to me! It took 2 and half weeks, a transfer to a regional children's hospital and a surgical tube in his chest to drain nearly 80mL of fluid that compressed his lung, due to the infection. He is home now and we are all doing well! Why I take some time to get back on my feet, attend to neglected contracts and projects, and regain some sense of normalcy, I'll be reposting some of my favorite past posts from my other blogs (edited for clarity).***

I’d like to tell y'all a little tale of a little shrimp from a little hydrothermal vent in a big ocean. You see, once upon a time I was a *real* marine biologist and got to go on lots of research cruises. Those were glorious days when I sailed out from exotic ports, drank the local flavors, backpacked around south Pacific islands and jammed with the crew up on top deck of research vessels under endless starry skies. The thrill of discovering something new always enticed me and I especially paid close attention to all the critters that were brought up from the depths. Years of observations and identifications has indeed twisted my mind so much that I dream about species. I seem to go about my daily routine as if it were being read from a dichotomous key (this may not be true).

I didn’t choose to find a new species of vent shrimp – it chose me. It was my first cruise for gathering material specifically for my masters thesis investigating how communities at deep-sea hydrothermal vents were structured. I was taking quantitative samples of mussel and snail beds for studying the role of foundation species in the vent community. Alvinocaridid shrimp are conspicuous members of these strange deep-sea environments and are found nearly worldwide. There are currently seven recognized genera. Alvinocarislusca was the first to be described by the late Drs. Austin Williams and Fenner Chace Jr. in 1982 and this genus contains the most species, with 11 recognized species as of time of publication (2009). Alvinocaris literally means “Alvin’s shrimp”. Alvin is the name of the submersible that was used when the first hydrothermal vents were studied (lusca means “blinded”, referring to it’s degenerate, fused eyes), also made famous for being used to study the wreck of the Titanic.

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This was an excellent species to learn taxonomy on. The characters were clear and unambiguous, few related species described to compare with, and my coauthor was a superb mentor who taught me many time-saving tricks while carefully coaching me to be a thorough, honest, and integrative scientist. The pieces really fell together with this species. The actual description of a species is very straight-forward and formulaic. The terminology has been in place for years. All that is needed is to fill in the blanks for your species and note any other distinguishing characteristics. Many taxonomists stop with the description and might add a paragraph of natural history notes. Naturally, I wanted to do more.

I felt it was important to understand the evolutionary context of this species. Thankfully, Dr. Tim Shank provided a comprehensive phylogeny of the shrimp family so GenBank was already populated with mitochondrial COI sequences. We sequenced a few individuals of our species, but the result wasn’t very clear. It appeared to be more basal to the genus, but statistical support wasn’t strong for its branch. In fact, COI appeared unreliable for clearing up the deeper relationships - a common problem with this molecule. A major multigene phylogeny is in the works by other colleagues that should clear up all the details in this important shrimp family.

[caption id="attachment_454" align="alignnone" width="491" caption="Map of known hydrothermal vent study sites, produced by Dr. Maria Baker of the ChEss programme (2010)."][/caption]

Why is this group of shrimp so important anyways? It turns out that all Alvinocaridids (that's family level for those keeping track) only live at chemosynthetic ecosystems, such as vents and methane seeps. The evolutionary history of this family should track their dispersal across the interconnected mid-ocean ridge system (see map above). Their endemicity to deep sea chemosynthetic environments makes them useful organisms to trace patterns of the historical dispersa of vent animals. In ecology, the unit of measurement is often the ‘species’, which is why it is important to describe and catalogue the distributions of all of Earth’s species. A more accurate prediction of historical processes can be determined as we add data to the tree of life.

My contribution will hopefully be useful to people working in vent biogeography and shrimp phylogenetics. To facilitate accurate identification of members of this shrimp family, I updated a dichotomous key of all 22 species that make up this happy crustaceous family.

The shrimp itself is really neat. A nice long, serrated rostrum adorns its head mimicking an 80s punk rocker loitering outside CBGB’s. The distinctive character that sets it apart from other Alvinocaris is a distinct notch in the middle of the tail, garnished with a nice set of spikes to puts Needleman to shame. My favorite part of writing this paper was making the line drawings. I took several detailed pictures under a dissecting microscope, mosaicked them together and traced the outlines in Adobe Illustrator, like below.

[caption id="attachment_455" align="aligncenter" width="300" caption="The 4th Pereopod (leg). High resolution, high magnification photos mosaicked together to form a sharp tracing image."][/caption]

This is corroborated by actually looking at it under the scope to make sure I got every little hair and spine! The photos are great, especially for someone like me that lacks any drawing ability whatsoever, but can be misleading because you may be out of focus for very fine details. This is why I corroborate my line drawing with the actual specimen under the microscope. Its very important to get the details right in a species description, drawings such as these below may be critical for a worker to compare their sample with the species' definition. The end result is a shrimp turned into art (in my humble opinion anyways!).

[caption id="attachment_456" align="aligncenter" width="600" caption="Alvinocaris komaii whole and line drawings of its body parts. Mouth parts (left, bottom) include from bottom Mandible, Maxillae 1 & 2, Maxillipeds 1-3. Pereopods (legs, bottom) 1-5 left to right, detail of the third pereopod given. An example of a Pleopod is given (right, middle), inset is the appendix masculina, or shrimp penis. The telson (right, top) the central part with the notch in the end, flanked by uropods. "][/caption]

Alvinocaris komaii is named after Dr. Tomoyuki Komai of the Natural History Museum and Institute, Chiba, Japan. It is a great honor to name a species after him. His extensive contributions have set the standard in descriptions of species in the family Alvinocarididae. Very thorough and accurate with detailed drawings and natural history observations. As he is nearing retirement, I was shocked to learn that he had not been yet honored by a specific epithet. It is appropriate then that a younger generation follow in his footsteps, but add on the techniques that we have “grown up” with,  such as phylogenetics.  There will always be a place for morphological systematics because species need a very specific definition if it is to be of use in evolutionary and ecological studies. The addition of genetics gives the individual being described a defined 'barcode' as well as a set of unique morphological characteristics appended to it, ensuring less ambiguity for future workers.

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Zelnio, K., & Hourdez, S. (2009). A New Species of Alvinocaris (Crustacea: Decapoda: Caridea: Alvinocarididae) from Hydrothermal Vents at The Lau Basin, Southwest Pacific, and a Key to The Species of Alvinocarididae Proceedings of the Biological Society of Washington, 122 (1), 52-71 DOI: 10.2988/07-28.1

*This post was originally posted in 2009 at Deep Sea News.