Abstract
Herein, we report the second known specimen of the one‐jaw eel, Monognathus jesse , collected in 4200 m of water, between 1748 and 2001 m depth, in the northeastern Pacific. This specimen is the second‐largest identified monognathid specimen reported, with a total length of 154 mm unpreserved. A morphological description, comparison to the much smaller holotype and similar species, a micro‐computed tomography scan, and mitochondrial sequences are provided. This specimen also represents a 3200 km northeastern range extension for the species, as the holotype was recovered 1050 km southeast of Hawai'i. A phylogeny of cytochrome oxidase‐I for this and related eel species recovers Monognathus as the sister to a clade comprising Cyema , Saccopharynx and Eurypharynx, contrasting previous hypotheses.