Prognathodes geminus is the Newest Species of Butterflyfish

Prognathodes geminus is the newest species of butterflyfish from a genus that haunts the abyssal depths of the oceans. Closely related to Prognathodes guezei and P. basabei, the new ‘Gemini’ butterflyfish is so named for its very close resemblance to other members of Prognathodes – indeed it takes very careful analysis and observations to distinguish several member of this genus.

The newly described Proganthodes geminus with a dark third dorsal fin spine

The very similar Proganthides basabei with a clearly whitish 3rd dorsal fin spine

The Prognathodes butterflyfish are, when they are rarely available, a very popular group with rare fish collectors, not just for their scarcity but also for their bold coloration and appearance. The freshly minted Prognathodes geminus is superficially identical to the deepwater Hawaiian orange-fin butterflyfish P. basabei.

The only visibly discernible difference between P. geminus & P. basabei is the coloration of the 3rd dorsal spine, being blackish brown in P. geminus and whitish cream in P. basabei. But genetically the difference between these two similar looking species is more divergent than between humans and chimpanzees.

Holotype of Prognathodes geminus in its natural habitat at a depth of 116 m off Ngemelis, Palau. Photo by J. L. Earle

The new Geminus or Gem butterflyfish was discovered in Palau at the bone-crushing depth of 116 meters, which is 380 feet, or more than double the safe limit for recreational SCUBA. The Gem butterflyfish was collected alongside the fabled Chromis abyssus and Abei angelfish and is documented in a famous 2007 deep diving video from National Geographic. The spankin’ new Prognathodes is described by Copus et. al. 2019 in the latest edition of ZooKeys.

Prognathodes guezei from deep reefs of the Western Indian Ocean

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Jake Adams

Jake Adams has been an avid marine aquarist since the mid 90s and has worked in the retail side of the marine aquarium trade for more than ten years. He has a bachelor’s degree in Marine Science and has been the managing editor of ReefBuilders.com since 2008. Jake is interested in every facet of the marine aquarium hobby from the concepts to the technology, rare fish to exotic corals, and his interests are well documented through a very prolific career of speaking to reef clubs and marine aquarium events, and writing articles for aquarium publications across the globe. His primary interest is in corals which Jake pursues in the aquarium hobby as well as diving the coral reefs of the world.