Hagfish

Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes, are eel-shaped jawless fish sometimes called slime eels. They are special because they are the only living animals with a skull but no vertebral column, though they do have very basic vertebrae.

These fish live in the marine world and act as both predators and scavengers. When they feel threatened, they can release a lot of slime from mucous glands in their skin to defend themselves against bigger animals.

Scientists once wondered how hagfish are related to another group of jawless fish called lampreys. Thanks to genetic research, we now know that hagfish and lampreys are more closely related to each other than to jawed vertebrates. This makes them part of a group called Cyclostomi. The oldest-known hagfish-like animals lived during the Late Carboniferous period, many millions of years ago, and modern hagfish have been found from the mid-Cretaceous period.

Physical characteristics

Hagfish are about 50 cm long, but some can be up to 127 cm. They look like eels with long, slender bodies and paddle-like tails. Their skin is soft and covers their body like a loose sock, and they are usually a dull pink color. They have simple eyes that can detect light but cannot see detailed images.

Hagfish can produce a lot of slime from special glands. When they release this slime into water, it expands quickly and can help them escape from predators by clogging the predator's gills. This slime is made of special proteins and can be very stretchy and strong.

Reproduction

Very little is known about how hagfish reproduce because many live deep in the ocean, making it hard to study them. In nature, there are usually more female hagfish than males, though this can vary between species. Some hagfish have both male and female reproductive parts before they grow up, and it is thought that females may develop earlier, which could explain why there are more females.

Female hagfish lay between one and 30 strong, fatty eggs. These eggs often stick together because they have special tufts on the ends, like tiny hooks. Scientists have a few ideas about how hagfish lay their eggs—such as in rocky crevices, under sand, or using their slime to keep the eggs in one place—but no one has seen this happen in the wild to confirm it. Unlike some other fish, hagfish eggs do not go through a special early stage called a larva before they hatch.

Hagfish embryos can take up to 11 months to develop before hatching, which is faster than many other jawless fish. Recent advances in caring for hagfish in labs have helped scientists learn more about their development and evolution. These studies show that hagfish share important cells with all other vertebrates, and they have a basic system that helps control their reproduction, similar to other animals. Some hagfish species reproduce at certain times of the year, triggered by hormones.

Feeding

Hagfish eat marine worms and can also feed on larger sea creatures that are dead or injured. They often go inside these creatures to eat from the inside. They can absorb food through their skin and gills, which helps them when food is hard to find.

Hagfish don’t need to eat often because they don’t use much energy. They have been found eating many types of sea animals, including shrimp, hermit crabs, and even sharks. Sometimes, they can be a problem for fishermen because they eat fish that are caught in nets before the nets can be brought to the surface.

Classification

Hagfish belong to a group of animals called Myxini and are part of the order Myxiniformes. They were once grouped with worms by scientists, but we now know they are special because they have a skull but no real backbone, though they do have tiny bits that act like vertebrae.

Scientists have studied hagfish for many years to understand how they are related to other animals. Some thought they were very different, but newer studies show that hagfish and lampreys are more closely related to each other than to other fish with jaws. This helps us see that hagfish are a type of very basic vertebrate, placed between animals without backbones and those with them.

Phylogeny

Hagfish belong to the group Cyclostomata, which includes jawless fish. This group is known for having special tooth plates and unique muscle movements. Scientists believe hagfish and lampreys separated from each other a very long time ago during the Paleozoic period. Studies using different methods suggest this split happened between 93 and 28 million years ago, with some newer studies pointing to even earlier times. Hagfish are different from another group called Gnathostomata because of their special body features, like their arched tongue. As hagfish grow, their bodies change dramatically.

Commercial use

As food

In many places, hagfish are not commonly eaten. However, in Korea, hagfish is a special food. It is usually skinned, coated in a spicy sauce, and then grilled or stir-fried. This food is very popular in places like Busan and other coastal cities in South Gyeongsang Province. Because hagfish is important in Korean cuisine, most hagfish caught around the world is sent to South Korea to be eaten. The inshore hagfish, found in the northwest Pacific, is also eaten in Japan and South Korea. The slime from hagfish can mix with a lot of liquid even when it’s cold, so it has been suggested as a way to save energy when making tofu without needing to heat it.

In textiles

The slime from hagfish can be turned into very strong fibers that can be used to make clothes. A scientist named Douglas Fudge, from Chapman University, has studied this idea.

Skins

The skin of a hagfish is often called “eel skin.” It can be used to make very strong leather, which is great for things like wallets and belts.