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.

1965年，波多黎各海沟的7300 m深度首次对海底深度的底栖动物群落的多样性和密度进行了首次直接观测。该报告中最引人注目的部分是在一个深水y鱼Archimède的1英里横断面上观察到200条fish鱼（Liparidae）的记录-一种极高密度的深海鱼。在2019年，潜水式DSV限制因素重新访问了波多黎各海沟中的同一地点。没有观察到鱼。但是，大量的全州Peniagonesp。看到的密度与最初报道的鱼相似。千足鱼的外观颜色，质地和形态与similar鱼相似。结论是，据报道波多黎各海沟的浅滩蜗牛鱼实际上是对全人类的Peniagone sp的错误识别。