https://phys.org/news/2019-01-fossilized-slime-million-year-old-hagfish-vertebrate.html

"This is a major reorganization of the family tree of all fish and their descendants. This allows us to put an evolutionary date on unique traits that set hagfish apart from all other animals," said Tetsuto Miyashita, Ph.D., a Chicago Fellow in the Department of Organismal Biology and Anatomy at UChicago who led the research. The findings are published this week in the Proceedings of the National Academy of Sciences.

Modern-day hagfish are known for their bizarre, nightmarish appearance and unique defense mechanism. They don't have eyes, or jaws or teeth to bite with, but instead use a spiky tongue-like apparatus to rasp flesh off dead fish and whales at the bottom of the ocean. When harassed, they can instantly turn the water around them into a cloud of slime, clogging the gills of would-be predators.