Olive Sea Snake vs Hagfish: What’s the Difference?

Written by Brandi Allred
Published: June 30, 2022
© DNC40/Shutterstock.com
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Our oceans are home to 99% of the living space on our planet. So it’s no surprise that two of the most interesting creatures on Earth—the olive sea snake and the hagfish—make their homes in entirely different parts of the ocean. The olive sea snake (Aipysuris laevis) is a member of the Elapidae family of snakes. Hagfish are members of the Infraphylum Agnatha; there are around 70 living species of hagfish known to science.

Read on to learn more about what differentiates an olive sea snake from a hagfish.

Comparing Olive Sea Snake vs Hagfish

The olive sea snake is a snake, while the hagfish is a fish.
Olive Sea SnakeHagfish
SizeUp to 6 feet long16-32 inches long
AppearanceMedium weight body with a flattened tail for swimming; gray to olive green in colorPale pink-gray, tubular bodies with no eyes. Flattened tails for swimming
Location and HabitatWestern Pacific Ocean; coral reefsAll of the world’s oceans; deep, cold ocean floor
BehaviorNonaggressive; inquisitiveProduces slime as a means of self-defense
Lifespan15-20 yearsEstimated 40 years

Key Differences Between Olive Sea Snake vs Hagfish

Hagfish Eptatretus hexatrema at the wreck of the Oakburn at Duiker Point on the Cape Peninsula
Hagfish live on the deep ocean bottom.

©Peter Southwood / CC BY-SA 3.0 – License

The key difference between the olive sea snake and the hagfish is that olive sea snakes are reptiles, and hagfish are fish. Olive sea snakes breathe air, whereas hagfish breathe water. Hagfish live on the murky ocean bottom and have no jaws, whereas olive sea snakes live among coral reefs and have jaws. Olive sea snakes are venomous hunters, while hagfish consume only the dead and small invertebrate creatures. 

Let’s take a closer look at the exact differences between the olive sea snake and the hagfish.

Olive Sea Snake vs Hagfish: Size

The Olive sea snake has special valves in its nose to keep water out while its swimming.
There is only one species of olive sea snake, which can grow to over six feet long.


Olive sea snakes grow to just over six feet long for the largest individuals. They have medium-weight bodies. There are around 70 different species of hagfish, with some growing to just over a foot long. The largest hagfish in the world grow to around 45 inches long.

Olive Sea Snake vs Hagfish: Appearance

Six gill hagfish Eptatretus hexatrema at the wreck of the Oakburn at Duiker Point on the Cape Peninsula
The hagfish lack eyes.

©Peter Southwood / CC BY-SA 3.0 – License

Olive sea snake and hagfish superficially resembles one another. Both are tubular creatures living in the ocean. However, that’s where the resemblance stops. Olive sea snakes have visible eyes, mouths, jaws and look like snakes with flattened, rudder-like tails. Hagfish, on the other hand, look like large, gray worms with small antennae on either side of their head. They’re the only creatures on Earth who possess a skull but no vertebral column.

Olive sea snakes are dusky tan to olive green in color, with pale bellies. Their heads are the same thickness as their bodies, which are streamlined for ocean travel. Hagfish also have flattened tails for swimming. They have eye dots but no actual eyes.

Olive Sea Snake vs Hagfish: Location and Habitat

Olive Sea snake, Disteira major in Bundaberg, Great Barrier Reef,Queensland. It can grow up to six feet long and weigh up to six and a half pounds.
Olive sea snakes occur only in the tropical western Pacific Ocean.

©Sahara Frost/Shutterstock.com

One of the biggest differences between the olive sea snake and the hagfish is where they live. Olive sea snakes occupy the warm tropical waters of northern Australia and New Guinea. There, they spend their lives hunting in coral reefs; they’re found nowhere else on Earth.

In contrast, hagfish are plentiful throughout the world’s oceans. But, they’re almost never seen by humans. This is because hagfish live only in deep, cold parts of the ocean. Some species live near shore; fishermen sometimes drag them in with their catch.

Olive Sea Snake vs Hagfish: Behavior

Hagfish, Duiker Point, Cape Peninsula.
Hagfish mainly consume already deceased creatures and small invertebrates.

©Peter Southwood / CC BY-SA 3.0 – License

Olive sea snakes are one of the only snakes on Earth that never come to land. Most sea snakes live in the ocean but come to land to lay their eggs. Not the olive sea snake. These truly aquatic snakes give birth at sea and never touch land. They’re highly venomous and are known to be curious about scuba divers. Bites to humans are very rare but can be life-threatening. Olive sea snakes eat small fish, fish eggs, and crustaceans.

Little is known about the reproductive methods of hagfish, other than they do appear to lay eggs. These creatures have also been known to bore holes in the sides of fish stuck in fishing nets, even while they’re still alive. On the ocean floor, they perform a vital service: cleaning up the dead. When threatened, they excrete a thick slime from pores in their body. The slime deters would-be predators.

Olive Sea Snake vs Hagfish: Lifespan

The Olive sea snake uses its tail like a paddle to propel it through the water in the coral reef biome.
Olive snakes can live up to 20 years.

©Gabriel Guzman/Shutterstock.com

These sea snakes are thought to live up to 20 years in the wild, a venerable age for a snake. Hagfish, on the other hand, have been recorded living up to 17 years in captivity. In the wild, however, they’re thought to live for around 40 years. But, little is known about the lifecycle of the wild hagfish, so they could live much longer than scientists think.

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About the Author

Brandi is a professional writer by day and a fiction writer by night. Her nonfiction work focuses on animals, nature, and conservation. She holds degrees in English and Anthropology, and spends her free time writing horror, scifi, and fantasy stories.

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