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‘Living fossil’ spider discovered in southern Sierra Nevada

Hypochilus_xomote.jpg
Courtesy of Marshal Hedin
The Hypochilus Xomote is a newly discovered species of spider that's native to the rocky landscapes of the southern Sierra Nevada, as seen here in an undated photograph.

The Hypochilus xomote looks like a common spider that you may discover at home. San Diego State biology professor Marshal Hedin said it’s a lot like the ubiquitous cellar spider, with its long legs and small abdomen.

“But if you look at it closely, it has this wonderful iridescence," he said. "I mean it’s quite different from a cellar spider and you would never find it in your house.”

You would find it in the cool, rocky canyons and caves of the southern Sierra Nevada mountains, not far from Bakersfield. Hedin and a biology master’s student were examining specimens in that region, in search of spiders from the Hypochilus genus. They knew the Hypochilus xomote was a new species when they compared it to existing spider genomes and discovered its genetic variation.

One striking thing about this spider and others in its genus: its morphology, meaning its appearance, has not changed for tens of millions of years.

“That’s called morphological stasis and the lineage goes back maybe 60, 80, maybe 100 million years,” he said. “Through that kind of expanse of time, the morphology has stayed in the same place, so it’s very much like a living fossil.”

The term “living fossil” gained popularity following the discovery of a fish, very much alive, called the coelacanth off the South African coast. This human-sized fish was first seen as a fossil, dating back hundreds of millions of years, and scientists had assumed it went extinct long ago.

Spider jars.jpg
Thomas Fudge
Samples of newly discovered species of the spider Hypochilus Xomote are seen in tiny jars, in the San Diego State lab of Marshal Hedin. May 19, 2022

Hedin said it’s too early to know whether his spider is endangered. He does say that the spider has a naturally small geographic habitat. It’s not threatened by development in its rural landscape, but it could be threatened by fire and climate change.

“They prefer cool, moist micro-habitats," he said. "So as those habitats become drier and hotter, then those are not places you would expect to find Hypochilus.”

Hedin said these kinds of spiders are often called “lampshade” spiders, because they build “beautiful” webs on rock walls that look like a lampshade.

The species that he and his grad student discovered was given the name xomote, which is a Yokut Indian word meaning “south.”