The Jawless Truth
Hagfish, often called “slime eels,” are jawless creatures. They belong to a primitive group of fish known as agnathans or cyclostomes, which are characterized by the absence of true jaws. This sets them apart from the vast majority of modern fish, which are jawed vertebrates (gnathostomes). Hagfish have an elongated, eel-like body that can range in color from pink to blue-grey. They typically grow to about 50 cm (19.7 inches) in length, though some species can reach over a meter.
Their skeletal structure is primarily cartilaginous, lacking a bony skeleton. Instead of a vertebral column, hagfish possess a flexible notochord, and they are the only known living animals with a skull but no true vertebrae, though they do have rudimentary ones. Around their mouth, they have six or eight whisker-like barbels, which they use for sensing their environment in the deep, dark waters where they live.
How Hagfish Feed
Hagfish have developed specialized feeding mechanisms that compensate for their lack of jaws. Their mouth contains two pairs of horny, comb-shaped teeth made of keratin, located on a protractible, tongue-like cartilaginous plate. These “teeth” move horizontally, allowing the hagfish to grasp food and draw it towards their pharynx.
These deep-sea scavengers primarily feed on dead or dying marine animals, often burrowing into carcasses to consume them from the inside out. To obtain leverage for tearing off flesh, hagfish employ a remarkable knotting behavior. They tie their flexible bodies into an overhand knot, which they then slide along their body to gain the necessary force to rip off chunks of food. This knotting ability is also used to remove the copious amounts of slime they produce as a defense mechanism, preventing self-suffocation. Hagfish can also absorb dissolved organic matter directly through their skin and gills, maximizing nutrient intake during infrequent feeding opportunities.
Evolutionary Significance
Hagfish represent a very early branch in vertebrate evolution, offering insights into the ancestral characteristics of this diverse group. Their lineage dates back at least 310 million years, with some studies suggesting divergence around 500 million years ago. Their jawless state is significant because it predates the development of jaws in other fish groups, making them a living example of a primitive vertebrate form.
Hagfish, along with lampreys, form the superclass Cyclostomi, which are the only surviving groups of jawless fish. While their exact relationship within the vertebrate family tree has been debated, genetic evidence strongly supports their close kinship. Studying hagfish helps scientists understand early vertebrate features and how key innovations, like jaws, emerged over evolutionary time.