With spindly arms and oversized claws, the newly discovered Otilioleptes marcelae lives in a seemingly inhospitable Patagonian lava tube and looks like a horrific monster straight out of a Ron Underwood flick. Then again, the arachnid is smaller than a coin and exhibits no venom to speak of.

Less terrifying and more intriguing, the “highly specialized” harvestman is a true troglobite, meaning its stark white pigmentation is an adaptation to a life spent confined to a cave, never seeing the light of day. Other adaptations, including elongated legs and a reduction of eyes, represent a new family of daddy long-legs and the first known troglobitic harvestman reported from Argentina.

Doña Otilia, a basaltic cave carved from ancient lava, is an “almost inconceivable” home for these arachnids. Lava tubes are relatively young structures formed by volcanic activity. As active lava flows from beneath the Earth’s crust, its outer layers harden when the lava comes into contact with the colder air. Inside, the lava continues to pour and eventually flow downwards and out, carving long tubes underground that may never see the light of day. Other harvestmen species have been seen in the region, with a few isolated populations found across Patagonian Argentina, but Doña Otilia lacks the moisture necessary for them to thrive.

Marcela Peralta, a cave biologist, collected several spider specimens while studying the 0.8-kilometer-long (0.5-mile-long) Doña Otilia Cave from 2006 to 2012, reports Gizmodo. They were then sent to zoologist and harvestman expert Luis Acosta at the National University of Cordoba.

“At first sight I thought I had juvenile specimens in my hands,” Acosta told the publication in an email. “They are normally useless for descriptive work, so I asked Marcela to ‘try to collect an adult male.’”

Their odd-shaped bodies and inability to see isn’t even the weirdest characteristic of the spiders. The arachnids lack sexual dimorphism, or a distinct difference in size between two biological sexes. At first, it appeared that all of the specimens collected by Peralta were juveniles. A closer look revealed that they were, in fact, all adults representing both sexes. In particular, males showed a uniquely shaped penis described in PLOS One as “elongated, very slender, and straight”.

Specialized species such as Otilioleptes can reveal information about the biogeographical and evolutionary characteristics of ancient species who thrive in such isolated environments today. Acosta believes that Otilioleptes may have split to its current lineage sometime between 11 and 16 million years ago.

With such unique pockets of species comes greater hazards. An “urgent need” to protect the new species and its cave environment is in order if scientists hope to learn more. Its delicate, isolated habitat means that even the slightest disturbance could alter the enigmatic species' life cycle forever.