A newly identified species of slender black moray eel prefers living in dark, muddy river mouths, a stark contrast to most of its ocean-dwelling relatives. This eel can be found throughout the Central Indo-Pacific region, including in the Puerto Princesa Subterranean River’s caves. The species is named after Hades, the god of the underworld, due to its distinctive habitat, peculiar behaviors, and especially its striking dark coloration.
The Hades’ snake moray (Uropterygius hades) is a slender, dark brown moray eel that thrives in the murky waters of river mouths, distinguishing it from most of its marine counterparts. It has a broad range in the Central Indo-Pacific, appearing in areas such as southern Japan, Taiwan, the Philippines, southern Java, and Fiji. The name Hades was chosen to reflect this moray eel’s unusual habitat, burrowing habits, high sensitivity to light, and, most importantly, its deep, dark skin tone.
Researchers Dr. Wen-Chien Huang, Dr. Rodulf Anthony Balisco, Dr. Te-Yu Liao from National Sun Yat-sen University in Taiwan and Western Philippines University, along with Dr. Yusuke Hibino from the Kitakyushu Museum of Natural History and Human History in Japan, describe this new species in a study published in the open-access journal ZooKeys. The name Hades points to its striking appearance and the murky regions it inhabits. This concept was inspired by Dr. Wen-Chien Huang’s thoughts on Ralph Fiennes’ portrayal of Hades in the film Clash of the Titans.
There are around 230 recognized species of moray eels worldwide, most of which live in marine environments. Only one species has been confirmed to primarily live in freshwater. Some marine eels, like the slender giant moray (Strophidon sathete), can withstand and occasionally venture into lower-salinity areas, such as river mouths. However, moray eels that are specifically adapted to estuarine habitats are extremely uncommon.
The discovery of the Hades’ snake moray was actually an unintentional finding. The three researchers from National Sun Yat-sen University were exploring the Puerto Princesa Subterranean River’s cave to survey aquatic life, specifically looking for a cave eel species called the bean-eyed snake moray (Uropterygius cyamommatus). This eel, known for its significantly reduced eye size, serves as a prime candidate for studying how eels have evolved to thrive in cave ecosystems. However, instead of discovering bean-eyed snake morays, the team found a slender moray with a strikingly dark and uniform color.
While in an aquarium, the Hades’ snake moray displays a unique tail-first burrowing behavior that is uncommon among moray eels. It’s also extremely sensitive to light, often trying to conceal itself when exposed. Its small eyes—likely an adaptation for low-light conditions—along with a reduced number of sensory pores on its head, which help prevent blockages from sediment, indicate that this eel may be a proficient burrower, relying mostly on chemoreception rather than sight to find food or evade threats.
