Roa rumsfeldi at the California Academy of Science. Credit: Luiz Rocha / Rocha et al. 2017

Slowly but surely, the undescribed butterflyfishes of the world are at long last getting the recognition they deserve. Last year, it was the Orangemargin Butterflyfish (Prognathodes basabei) that was given a proper scientific name after decades of anonymity, and the newest to join rank is Roa rumsfeldi, a species that’s been known to aquarists for a little while now.

Unless you happen to be proficient at mixed-gas rebreather diving, you’d be hard pressed to find this fish anywhere outside of the California Academy of Sciences’ spectacular Twilight Zone: Deep Reefs exhibit. Lead by the eminent mesophotic explorer, Dr. Luiz Rocha, a team of researchers succeeded in bringing a specimen back alive from an expedition to the Philippines, and it was only when observed within the confines of an aquarium that the subtle differences of this fish were truly appreciated.

You can read a bit more about what makes this fish unique in Lemon’s excellent review of this genus here, or his expose on the Steinhart’s specimen here. Roa species all share a similar blueprint, but the morphology of the dorsal fin, the relative shape of the head, and some minor nuances of the color pattern diagnose R. rumsfeldi as distinct. To date, it has only been found in the Philippines at depths of 100 meters or more, though, in all likelihood, it can be expected to occur broadly in the Coral Triangle.

There is a rather poignant etymology for this fish which stems from a famous quote by former politician Donald Rumsfeld. As the authors put it…

We name Roa rumsfeldi to honor Donald Rumsfeld who immortalized the quote: “there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know.” He said that when referring to the uncertainties of war, but we think it applies perfectly to the taxonomy of MCE species: We only realized this species was new after we took a good look at it here at the aquarium in San Francisco, so we think it’s a perfect example of an unknown unknown.

Unfortunately, there was no common name suggested for this species. The natural tendency would be to name it after Mr. Rumsfeld, but, as he already has a perfectly good slime-mold beetle to honor his contributions, I think it more fitting that this lovely fish should instead pay homage to his masterful wordplay… the Unknown Butterflyfish is emblematic of all the ocean’s mysteries and our ceaseless search to reveal their secrets.

• Rocha L, Pinheiro H, Wandell M, Rocha C, Shepherd B (2017) Roa rumsfeldi, a new butterflyfish (Teleostei: Chaetodontidae) from mesophotic coral ecosystems of the Philippines. ZooKeys 709: 127-134. https://doi.org/10.3897/zookeys.709.20404