Revisiting the 1964 Archimède bathyscaphe dive to 7300 m in the Puerto Rico trench, abundance of an elasipodid holothurian Peniagone sp. and a resolution to the identity of the ‘Puerto Rican snailfish’

The first direct observations of the diversity and density of benthic epifauna from hadal depths was reported in 1965 from depths of 7300 m in the Puerto Rico Trench. The most striking part of the report from was an account of observing 200 snailfish (Liparidae) during a one mile transect by the bathyscaphe Archimède - an extraordinarily high-density of fish for hadal depths. In 2019 the submersible DSV Limiting Factor revisited the exact same site in the Puerto Rico Trench. No snailfish were observed. However, a large number of the holothurian Peniagone sp. were seen in a density similar to that reported originally for the snailfish. The holothurian has a similar exterior colour, texture and morphology to the snailfish. It is concluded that the reported hadal snailfish of the Puerto Rico Trench was in fact a misidentification of the holothurian Peniagone sp.