What is "bathysoma"

Bathysoma lutkeni ("Lutken's Deep Body") is an extinct lamprid from the Danian epoch of Sweden, and is the second oldest lamprid known, after Nardovelifer of Campanian/ Maastrichtian Italy. B. lutkeni has a disk-shaped body and an elongated head. It was originally described as a menid bony fish. Later, it was described as being a basal snake mackerel. Eventually, anatomical similarities with the Turkmenids were noted, and B. lutkeni is now regarded as an extremely basal lamprid.