Tiny, Alien-Looking Subterranean Catfish Puzzles Scientists

| 15 May 2014 14:50

Catfish on the outside, Xenomorph on the inside.

After discovering a new species, scientists work to classify it based on the characteristics is shares with other organisms, a branch of science known as taxonomy. Kryptoglanis shajii, a tiny catfish first described in 2011, is puzzling the scientists who are working to classify it. Kryptoglanis looks like a typical catfish on the surface, but digital radiography and high-definition CAT scans revealed that its bone structure is very different from other catfishes. "The characteristics of this animal are just so different that we have a hard time fitting it into the family tree of catfishes," says John Lundberg, emeritus curator of Ichthyology at the Academy of Natural Sciences of Drexel University and emeritus professor at Drexel in the College of Arts and Sciences. The researchers were unable to determine which other catfishes are the closest relatives of Kryptoglanis.

Lundberg is an expert on catfishes, and he and his team published the results of their work on Kryptoglanis on May 13, in the 2014 issue of the Proceedings of the Academy of Natural Sciences of Philadelphia. The catfish's skeleton is missing several bony elements, and its face is compressed and has a jutting lower jaw, rather like a bulldog. Lundberg describes these changes as "completely unique among catfishes and all fishes as far as I know." The researchers examined three specimens using digital radiography, and one of those specimens was also examines used high-resolution X-ray computed tomography. That provided three-dimensional CAT scan images of the tiny catfish skeleton. A video visualization of the skeleton was produced from these scans.

The tiny catfish is subterranean, appearing rarely in flooded rice paddies, springs, and wells in Kerala, India. With four rows of sharp teeth, Kryptoglanis's skeleton looks like something out of Alien, but the catfish is only about the size of an adult's pinkie finger. Lundberg says that Kryptoglanis is likely a meat eater, feeding on insect larvae and small invertebrates found in groundwater. The compressed face and jutting jaw that makes Kryptoglanis different from other catfishes may have a functional purpose. Multiple changes in one part of the body can suggest an adaptation to evolutionary pressures. "In dogs that was the result of selective breeding," says Lundberg. "In Kryptoglanis we don't know yet what in their natural evolution would have led to this modified shape."

A separate team of researchers led by Ralf Britz at the Natural History Museum of London also examined Kryptoglanis's bone structure, using a technique called clearing and staining. The technique leaves the flesh and other soft tissues see-through, while the bones and cartilage are stained bright colors. Britz's team published its findings in March 2014, in the journal Ichthyological Exploration of Freshwaters. "There was an amazing congruence between the results," says Lundberg. "Neither of us was way out."

Source: Proceedings of the Academy of Natural Sciences of Philadelphia

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