Thousands of meters below the surface of the Atlantic Ocean, a submersible glided through the dark waters. An orange sea monster with its five arms spread wide sat enthroned on a nearby seamount.

The bumpy animal turned out to be a new species.

Researchers aboard the National Oceanic and Atmospheric Administration ship Okeanos Explorer set out to explore the depths of the Atlantic Ocean using remotely operated vehicles, Christopher Mah wrote in a study published April 3 in the peer-reviewed journal Zootaxa.

During their 2021 expedition, the researchers encountered several “pale orange” starfish, the study says. They collected one starfish and photographed several more.

Mah analyzed the orange starfish and found that they had discovered a new species: Rhianastra isosceles, or Rhian’s isosceles starfish.

Rhian’s isosceles starfish typically have five “sharply triangular” arms, but one animal had six arms, the study says. The starfish are covered with “rough, round” bumps.

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A photo shows the cream-orange new species next to some sandstones. Mah said he named the new species “isosceles” after its “distinctive triangular arms.”

Rhian’s isosceles starfish were found at depths of 1,740 to 1,980 meters, the study said.

The new species is part of a new genus called Rhianastra, named after Rhian Waller, a researcher and leader of the expedition that collected the specimen.

“Another species of this genus has been found in the Pacific,” Mah wrote on X, formerly Twitter.

So far, Rhian’s isosceles starfish has only been found on two seamounts in the North Atlantic, the study says. The seamounts are located about 700 miles east of the Delaware coast.

The new species was identified based on its body shape, arms, texture and other subtle physical characteristics. The study did not provide DNA analysis of the new species.

Mah also discovered another new starfish species, Bathyceramaster kelliottae, and identified several other starfish that may be new species.

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