In my earlier blog, I set up the context for the discovery of a new species of giant file clam in the northwest Atlantic in collaboration with colleagues from Fisheries and Oceans Canada. I want to emphasize that assigning a name to a specimen (one aspect of taxonomy) is a dynamic thing. While we do our best to review the scientific literature and examine as many specimens as possible, it is not rare that a re-examination of or access to more information can lead to a different conclusion.
In the case of our new giant file clam, we needed more specimens from our waters to compare with the European species (that we originally assumed our specimen to be), and we needed more of the latter, too. So, we borrowed material from three European natural history museums (Belgium, Bergen and Copenhagen). We sent a graduate student to the Smithsonian and to the American Museum of Natural History. We obtained new specimens from the Gully Marine Protected Area and the Flemish Cap area (northeast of the Newfoundland Grand Bank, in collaboration with a Spanish expedition).
Finally, we had images of 152 specimens for our morphological analysis.
But the problem with most giant file clams is the fact that they do not display many distinguishing morphological characters. They have a fairly oval-shaped shell with a somewhat simple hinge, an oblique V-shape ligament pit (visible in the top right portion of Figure 2), and some faint radial ribs on the external side of the valves. As a result, trying to compare species based on traditional morphometrics (e.g., shell length vs. shell width, hinge length, etc.) was not going to reveal much.
So, we resorted to use a relatively recent statistical approach called “Shape Analysis”. With this, we can actually describe the shape (contour) of each shell and quantitatively compare them within and between species.
This analysis—which required months to acquire the images, extract the 2-D shape data and do the comparisons—confirmed that adult (i.e., non-larval) specimens found in the northwest Atlantic are morphologically very similar to those from the northeast Atlantic. With only that data in hand, we would probably conclude that our specimens are at least marginally representative of the European giant file clam and could not be considered a different species. Fortunately, my DFO colleagues were able to extract fresh tissues from some of the newly collected northwest Atlantic specimens to do DNA Barcoding.
This new data was then compared to published barcodes from the European giant file clam species, two species from the Gulf of Mexico and two species from the northeast Pacific. The result: a significant genetic difference, amply sufficient to place our specimens under a new species. We named it Acesta cryptadelphe, which means the “cryptic sibling”, because of its strong morphological resemblance to the European species.
So, after all of this, we now have a new species. But why should we get excited about one new species? The fact is: we know that there are plenty of species on this planet that have yet to be discovered. In an environment like the deep sea, only a fraction of what lives there has been described. Many of the species names we assign to organisms (that look like they are already known to science) may well be incorrect. The new cryptic species of giant file clam from the northwest Atlantic is a good example of that. And if we want to understand and protect our ocean biodiversity, we really need to know what it is made of. In fact, the Gully received the designation of Marine Protected Area in May 2004 particularly because of its high biodiversity. And this study shows that we are just scratching the surface.
Read Part 1 of Jean-Marc’s story about the giant file clam: