Scientists hoped they'd find some exotic creatures burrowing through some of the deepest caves in Croatia, and they did not come up short. Meet Geophilus hadesi—or "Hades," named for the Greek god of the underworld—a subterranean centipede discovered in the Velebit mountain range by the Croatian Biospeleological Society, per a press release. The carnivore eats other invertebrates and also shows some longer-than-average legs and antennae (which help it find prey in total darkness, LiveScience notes), as well as jaws filled with poison. But what really makes this "centipede from hell" unique is that it's one of "only two remarkably troglomorphic geophilomorphs hitherto known," per the study in ZooKeys. Translation: It's one of only two centipede species that never leaves its cave dwellings, earning it its alternate title of "king of the underworld."
And Hades has a queen, too, who never leaves her own underground domicile: Geophilus persephones, or "Persephone," named for the Greek goddess of the underworld, per LiveScience. That species was discovered in southern France in 1999, the study notes. Hades has a couple of features that scientists believe emerged as evolutionary adaptation traits, including long claws at the end of its 33 pairs of legs (perhaps so it can cling to rocks) and the ability to withstand the caves' chilly temps, which can hover in the 30s. How they migrated to these underground dwellings in the first place isn't certain, but the lead author of the study tells LiveScience that it could have been "a dramatic change in the outside temperatures and overall conditions that forced less-adaptive organisms to seek shelter underground where the conditions are more stable and less dependent on the outside fluctuations." (A centipede bite could provide more pain relief than morphine.)