Quite possibly the most aptly named animal on the planet, here is Monterey Bay Aquarium’s description of the truly foul hagfish.
Also known as slime eels, hagfish are primitive fishes. They have four hearts, no jaws, no true eyes and no stomach. They have poor vision but a very good sense of smell and touch.
Hagfish live in burrows on the seafloor and locate their food by smelling and feeling as they swim. They prey on small invertebrates living in the mud, as well as scavenging dead and dying fish. They are noted for their unusual way of feeding—they slither into dead or dying fishes and eat them from the inside out, using their “rasping tongue” to carry food into their funnel-shaped mouth.
Hagfish are notorious for their defensive slime––a mucous fluid secreted from their pores. It’s different from slime that some other fish produce; millions of microscopic threads run through it, which makes it extremely sticky.