Pacific Hagfish (Eptatretus stoutii)
Hagfish have elongated, eel-like bodies (though they are not eels), and paddle-like tails. They have cartilaginous skulls (without jaws) and tooth-like structures composed of keratin. Colors depend on the species, ranging from pink to blue-grey, and may have black or yellow spots. Eyes may be vestigial.
(Though they are vertebrates, they are very different from bony fishes, being much more primitive.)
When captured and held by the head, they escape by secreting the fibrous slime, which turns into a thick and sticky gel when combined with water, and then cleaning off by tying themselves in an overhand knot which works its way from the tail to the head of the animal, scraping off the slime as it goes. Hagfish enter both living and dead fish, feeding on the insides. While having no ability to enter through skin, they often enter through natural openings such as the mouth, gills or anus and consume their prey from the inside out…
(read more: Oregon Coast Aquarium)