Sea Hagfish

The sea hagfish (Myxine glutinosa) is a jawless fish in the family Myxinidae, one of the most primitive living vertebrate lineages, often called a 'living fossil' because its body plan has changed little in hundreds of millions of years. It lacks true jaws, a backbone, and paired fins, relying instead on a cartilaginous skull and a rasping tongue-like structure to feed. Sea hagfish are found on both sides of the North Atlantic, from the Barents Sea and Norway to the eastern coast of North America, living on cold, muddy or sandy bottoms of the continental shelf and slope. They are best known for their ability to release huge volumes of thick defensive slime within seconds when disturbed or attacked.

• Elongated, eel-like, scaleless body, usually pinkish-grey to brownish-purple
• No jaws, no paired pectoral or pelvic fins, only a low continuous tail fin
• Slit-like mouth ringed by short sensory barbels, no visible eyes
• Row of small external gill pores running along each side of the body
• Skin studded with slime-gland pores that ooze mucus when handled

Sea hagfish are distinguished from true eels and lampreys by their complete lack of jaws and paired fins, their smooth scaleless skin, and the row of gill pores rather than gill slits. Unlike lampreys, they have no circular sucker-disc mouth and no dorsal fin rays.

Sea hagfish inhabit the cold, dark seafloor of the North Atlantic, ranging from Arctic Norwegian waters south to the Mediterranean on the eastern side and from the Gulf of Maine to Florida on the western side. They occur on muddy or sandy continental shelf and upper slope bottoms, typically between about 20 and 1,100 meters deep, though they are most common in the range of 100 to 500 meters. They favor soft substrates into which they can partially burrow, and are tolerant of near-freezing water temperatures. Sea hagfish avoid brightly lit shallow water and are rarely encountered by divers, instead being most often collected in baited traps set on the deep continental shelf.

Sea hagfish are solitary, nocturnal scavengers that spend much of the day buried in soft sediment with only the head exposed, emerging to feed on dead or dying fish, worms, and other invertebrates that sink to the seafloor. When threatened, a hagfish releases fibrous, protein-based slime that expands massively in seawater, clogging the gills of would-be predators. They can also tie their own bodies into a knot to scrape off slime or gain leverage while feeding, sometimes burrowing into a carcass to feed from the inside. Sea hagfish are simultaneous hermaphrodites, functioning as both sexes, and lay small numbers of large, yolky, tough-shelled eggs on the seafloor rather than undergoing a larval stage.