Taxonomist assessment: John Yeh (UH) - The synaphobranchid observed by MBARI on T945 at Davidson Seamount looks like either Histiobrachus bathybius or Ilyophis arx. I (Dr. Yeh) collected both species in NWHI in 2009. In photographs they look very similar - both having very small round pectoral fins and dorsal insertion is level with the pectoral fins. However, looking at both specimens side by side they differed most distinctly by gill slits. I. arx has small distinctly separated gill slits while openings in H. bathybius are larger and almost confluent. They also differ in in head pore counts and dentition (not visible in in situ video or images). They occur similar depths.
ReferencesEncyclopedia of Life
Tree of Life
World Register of Marine Species
National Center for Biotechnology Information
Citation: Synaphobranchidae Deep-Sea Guide (DSG) at http://dsg/mbari.org/dsg/view/concept/Synaphobranchidae. Monterey Bay Aquarium Research Institute (MBARI). Consulted on 2021-01-17.