The Mariana hadal snailfish, Pseudoliparis swirei, a recently described snailfish species living below a depth of 6,000m in the Mariana Trench. P. swirei has transparent unpigmented skin and scales, thin and incompletely ossified bones, an inflated stomach, and a non-closed skull. The hadal snailfish are top predators in the hadal food web and dominate the hadal fish fauna.