Hagfish

• Faced with a threat it releases a secretion that, on contact with water, expands within seconds, turning several litres into a dense gel that clogs the attacker's gills; its fibres are being studied for making technical textiles.
• To rid itself of its own slime and to tear off mouthfuls it ties its body in a knot and runs the knot from head to tail.
• It has no jaws and no true vertebrae, though it does have a skull, and its position in the vertebrate tree makes it a key piece in understanding our own origins.
• It produces the most extraordinary slime in the animal kingdom: when attacked it releases a secretion that, on contact with seawater, expands up to 10,000 times its volume in fractions of a second, generating litres of a gelatinous mass that chokes and clogs the gills of the predator.
• That slime is no simple mucus: it contains protein threads of up to 15 cm coiled inside specialised cells, which unfurl and form a three-dimensional network. It is being investigated as a model for strong, biodegradable synthetic fibres, and also for anti-ballistic materials.
• And it knows how to rid itself of its own slime: it ties itself into a knot and slides the loop along its body to wipe itself clean.
• It eats carrion from the inside: it slips into the carcass of a fish or a whale through any opening and consumes it from within. It also absorbs nutrients directly through its skin and gills, something unique among vertebrates.
• It has no vertebrae, no jaws and no paired fins. It is one of the two surviving lineages of jawless vertebrates, alongside the lampreys, and its anatomy is key to understanding the origin of vertebrates.
• It has four hearts and can survive for hours with almost no oxygen.

Skeleton type

Vertebrate - cartilaginous skeleton without vertebrae (hagfish)

Habitat and environment

Muddy bottoms of the North Atlantic, between 20 and 1,000 m

Sources consulted: https://es.wikipedia.org/wiki/Myxine_glutinosa