Some like it hot: The enigmatic Arctic deep-sea eelpout Pachycara platyrhina thrives at hydrothermal vents

For more than 100 years, information on the Arctic deep-sea eelpout Lycenchelys platyrhina (Jensen, 1902) has been based on a single small specimen, leaving uncertainty as to its generic assignment and very limited data on its distribution and ecology. With the addition of 14 specimens collected in recent decades, we here provide a re-description of the species and add information on its biology. Based on a combination of morphological characteristics and molecular data, L. platyrhina is reassigned to the genus Pachycara . It is found to be most similar and closely related to congeners P. microcephalum (Jensen, 1902), P. saldanhai (Biscoito & Almeida, 2004) and P. thermophilum (Geistdoerfer, 1994) occurring on or near the Mid-Atlantic Ridge. While Pachycara platyrhina is occasionally observed on muddy sediments, it appears to be quite abundant at hydrothermal vent sites, in tubeworm forests and even resting in warm water on or near hydrothermal chimneys. It represents the first known high Arctic member of Pachycara and we hypothesize it colonized the Arctic Ocean from the Atlantic and not from the North Pacific as assumed for most Arctic zoarcids.