Nemertea, also known as ribbon or proboscis worms, is a phylum of invertebrates living in marine and freshwater waters worldwide. They use their muscular proboscis to capture their prey. Up to now, experts have described approximately 1,000 species, but they will likely describe a few hundred more soon.

From what we already know, most species are tiny, inconspicuous inhabitants of the coastal waters. However, they are active predators that feed on various small animals, including plankton.

Despite their simple appearance, Nemerteans are highly diverse and have evolved a range of specialized adaptations to suit their particular environments and lifestyles. That’s why some are only found in Polar Regions or hydrothermal vents, while others are more widespread and can be found in various habitats. Read on for more about these soft-bodied worms.


Nemertea is characterized by their long, slender bodies, which are often ribbon-like in appearance. Their soft bodies are composed of three distinct layers:

  • An outer epidermis
  • A middle layer of muscles
  • An inner layer of connective tissue

Most species have a distinct head region featuring a specialized feeding part called a proboscis. The proboscis is used to capture and immobilize prey and is often armed with sharp, chitinous hooks.

The smallest species are less than a centimeter, while the longest, the bootlace worm, can grow to over 50 meters.

Another striking feature of Proboscis worms is their coloration, ranging from bright, vivid hues to muted tones. Some have intricate patterns and markings on their bodies, while others are a single solid color.


Nemertea is found in many marine and freshwater habitats, including shallow coastal waters, deep sea trenches, and even freshwater lakes and streams. Some species attach themselves to hard surfaces, such as rocks or coral, using a specialized glandular adhesive pad.

In short, the specific habitat requirements of Nemertea can vary depending on the species, with some preferring sandy or muddy bottoms and others preferring rocky or coral reefs. They are found in warm and cold water environments and can tolerate various salinity levels.


Nemertea feeds on sea animals such as small fish, crustaceans, and other invertebrates. They are renowned scavengers and hunters with a unique feeding strategy involving using their long, muscular bodies to capture and immobilize their prey. It coils around the prey and swallows it whole.

Sometimes, they produce a sticky or poisonous substance and use it to trap and immobilize their potential meal. When the worms deem it safe, they use their muscular body to drag the prey toward their mouth and swallow it.


Nemertea has a variety of reproductive strategies, depending on the species. Some species reproduce asexually by splitting into two or more pieces that can regenerate into new individuals. Others reproduce sexually, with males and females releasing their gametes into the water column for external fertilization.

In some species, such as Lineus longissimus, the male will deposit a specialized sperm sac on the female’s body. When the sperm comes into contact with the eggs, they get fertilized.


While Nemertea are soft-bodied worms, they have few natural predators. Their toxic secretions are excellent predator deterrents.

Nemertea discharges sticky secretions in response to a perceived threat
Nemertea discharges sticky secretions in response to a perceived threat

Better still, most of them can regenerate parts of their lost bodies, which is a perfect way of surviving attempted predation.

These species face some risks due to habitat destruction, overfishing, pollution, and climate change.

In some areas, commercial fishing is the most conspicuous concern. Remember that Nemertea is a delicacy in some cultures. Besides, commercial fisheries use it as bait.

Introducing non-native species, which can outcompete or prey upon native populations, is another crucial threat. For example, the invasive comb jelly Mnemiopsis leidyi has been shown to significantly impact the distribution and abundance of Nemertea in some areas.

Facts About Nemertea

  1. Nemertea is also known as ribbon worms because of their long, ribbon-like bodies.
  2. They are found in marine and freshwater habitats worldwide, including deep sea trenches and freshwater lakes and streams.
  3. Nemertea feed on a wide range of prey, including small fish, crustaceans, and other invertebrates.
  4. Some species of Nemertean reproduce asexually by splitting their bodies into two or more pieces that can regenerate into new individuals.
  5. Others reproduce sexually, with males and females releasing their gametes into the water column for external fertilization.
  6. Nemertea has a well-developed proboscis, which they use to capture and immobilize their prey.
  7. They can tolerate varied salinity levels and water temperatures.


What is the size range of Nemertea?

Nemertea varies significantly in size depending on species, habitat, diet, and other factors. Their size range from less than 1 millimeter to over 30 meters. However, most species measure between 5 and 10 centimeters. Note that some of the smallest species are found in freshwater habitats, while the largest is in salty habitats.

Can Nemertea reproduce asexually?

Yes, some species of Nemertean can reproduce asexually by fragmentation. This process involves the worm splitting into two or more fragments, each of which can regenerate into a complete and viable individual. This process allows these species to rapidly increase their population size and colonize new habitats without needing a mate. However, others like Lineus longissimus require a mate.

Can a Nemertea paralyze you?

Some species of Nemertean produce toxins that can paralyze their prey. While these toxins are typically only harmful to small invertebrates, they can cause skin irritation, itching, and redness in humans. So, these worms might not paralyze you. Nevertheless, you should handle them carefully to protect yourself from any injury.

How long can Nemertea live

The lifespan of Nemertean can vary greatly depending on the species and environmental conditions. For example, the giant ribbon worm, Lineus fuscoviridis, can live for up to 25 years in the wild. Nevertheless, the smaller species typically live in the wild for less than 10 years. So, there is no specific age limit since the lifespan of a Nemertean can vary widely.

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