Using an innovative method for peering inside soft-bodied animals, researchers have described a new species of leech and named it after best-selling author Amy Tan.
Chtonobdella tanae, a terrestrial leech from Australia, is the first new species of invertebrate without chitinous or calcified tissues (like a shell or exoskeleton) to be described using computed tomography (CT) scanning. The work was recently published in the journal Zoologica Scripta, and represents a new avenue for studying soft-bodied organisms like worms and jellyfish—especially those like Chtonobdella tanae which, at about 1 centimeter long and 2 millimeters wide, is too small to dissect.
“Historically, to get an idea of what the internal structure of a soft-bodied invertebrate looks like, you have to dissect it by hand or painstakingly section the specimen and then reconstruct it in three dimensions,” said Michael Tessler, lead author on the paper and a student in the comparative biology doctoral program at the Museum's Richard Gilder Graduate School. “CT imaging is not only more precise than physical dissection, but it also doesn’t require us to destroy the specimen we’re studying.”
CT scanners take thousands of cross-sectional x-ray “slices” of a rotating object to produce a digital 3D view of its interior. As the x-ray beam passes through the object, different tissues or materials absorb different amounts of x-rays. Detectors on the opposite side pick up the x-rays and create a contrast image based on the density of the internal components.
As with all x-ray techniques, dense structures like bone are easily imaged, whereas soft tissues are less able to stop x-rays, making them difficult to image. The result is that while CT scanning has enabled great strides in fields like paleontology in the last decade, those who study soft-bodied organisms have continued to rely on traditional dissection techniques to examine their specimens.
With the goal of making the tissues in soft-bodied animals show more contrast in CT scans, the researchers examined a variety of chemicals that preserve biological tissues from decay. Tests revealed contrast in the CT image was best enhanced by treating the leech with a compound called AFA, and then treating it again with the chemical osmium tetroxide. This two-step process let the heavy metal osmium bind to the specimen’s internal tissues, making it easier to image in a CT scanner.
Watch the video of the CT Scan of the leech named for Amy Tan.
“We were able to resolve the external and internal anatomy at very high resolution,” said co-author Mark Siddall, a curator in the Museum’s Division of Invertebrate Zoology. “In addition, we were able to see internal structures we might not have otherwise seen because of the disruptive influence of cutting things open.”
The leech was given the name Chtonobdella tanae in recognition of Amy Tan, author of the best-selling novel The Joy Luck Club and other works, who was excited to hear about the honor.
“I am thrilled to be immortalized as Chtonobdella tanae,” Tan said. “I am now planning my trip to Queensland, Australia, where I hope to take leisurely walks through the jungle, accompanied by a dozen or so of my namesake feeding on my ankles.”