A small toothed fish looking like something out of the "Alien" series of films has scientists puzzled, even baffling attempts to decide what species is should be classified as.

A tiny catfish with an odd bony face, Kryptoglanis shajii, lives mostly underground in just one area of a range of mountains in India, only rarely surfacing above ground in wells, springs and in rice paddies when they are flooded.

It was so rarely seen that it was only in 2011 that scientists decided it qualified as an entirely new species, although exactly where it belongs in the catfish world remains a puzzle, they say.

"The more we looked at the skeleton, the stranger it got," says ichthyologist John Lundberg of Drexel University in Philadelphia. "The characteristics of this animal are just so different that we have a hard time fitting it into the family tree of catfishes."

Although externally it looks like several other species of catfish, when Lundberg and colleagues performed high-definition X-ray scans of its bone structure, they were not prepared for what they found.

Four rows of sharp teeth inhabit bulging jaws that give the fish the look of a bulldog, they discovered.

The look is different from that of any other catfish, or from any kind of fish known, the researchers say. If there is in fact a specific purpose or function behind the strange facial configuration, it's not yet apparent, they add.

"In Kryptoglanis, we don't know yet what in their natural evolution would have led to this modified shape," Lundberg says.

It's likely not the result of some highly specialized or limited diet, the researchers said, since the teeth suggest typical underground food sources such as insect larvae and small invertebrates.

Videos of live Kryptoglanis specimens suggest the tiny, 4-inch fish are capable of catching and eating such prey, they said.

Lundberg and his colleagues are not the first scientists to focus on the odd fish; a separate study led by the Natural History Museum of London also looked at its unusual bone structure, using chemical means to render colored views of the skeleton rather than the X-ray scans of the Lundberg-led study.

Lundberg and his co-researchers have published their study in the Proceeding of the Academy of Natural Sciences of Philadelphia.