What is a sea cucumber?

Sea cucumbers are one of the strangest-looking creatures you will find in the sea. These marine invertebrates are echinoderms from the class Holothuridea. They have an oblong-shaped body and they live on the seafloor. There are around 1,717 known species of the sea cucumber. They are found in every ocean around the world, both in the shallows and the deep seas. While these worm-like sea creatures may look unusual, they are actually pretty amazing.

Here are 10 amazing facts about the sea cucumber that will blow your mind.

1. Sea cucumber poop is vital to the ecosystem and can help save coral reefs.

Sea cucumber poop is vital to a healthy ecosystem. Sea cucumbers have a pretty cool digestive system that is able to filter their food. The byproduct that comes out is full of nutrients that are beneficial for coral formation. One of the nutrients found in sea cucumber poop is calcium carbonate. This element not only helps corals grow their exoskeleton, it also increases the alkalinity of the water. That means the reef where sea cucumbers live is protected from localized acidification.

sea cucumber poop
Image by GIPHY

2. Sea cucumbers can poop the equivalent of 5 Eiffel towers in weight in one year.

Sea cucumbers poop A LOT. But because their poop is a natural fertilizer for the reef, that’s actually a great thing! According to one research, one sea cucumber poops out about 1.3 ounces of poop every day or 30.8 pounds a year. An experiment was done in Heron Island reef in Australia to measure how much poop sea cucumbers make. The research concluded that sea cucumbers in this reef alone could poop an equivalent of 5 Eiffel towers in mass in just one year.

3. Sea cucumbers breathe through their butts through a unique respiratory system.

Sea cucumbers have a very unique respiratory system. They breathe by dilating their anal opening and sucking water in. Inside the rectum is the respiratory tree. This is a lung-like structure, or a “butt lung”, that filters the water and extracts the oxygen molecules from it. When the sea cucumber is clenching its butt, it is also pretty much holding its breath.

4. Some species of parasitic fish live in the sea cucumber’s anus.

There is just so much going on with this sea creature’s butt! It is also home to a parasitic fish called pearlfish. With its slender, eel-like body, the pearlfish swims inside the sea cucumber and takes shelter. They do this by waiting for that opening when the sea cucumber breathes and sucks in water. A sea cucumber can house multiple pearlfish in their anus. Some have five or even more!

the pearlfish swims inside the sea cucumber
Image by GIPHY

Some sea cucumber species have developed “anal teeth” to ward off potential inhabitants.

Most sea cucumbers don’t have a problem being a host to inhabitants because they don’t really negatively affect them. There are other more rare sea cucumber species, however, who have developed anal teeth to keep unwanted guests away.

5. When threatened, the sea cucumber defense mechanism is to expel their guts.

While they may be slow-moving and have soft bodies, the sea cucumber defense system is pretty amazing. They have a couple of unique ways to shoo away predators. One of the best known sea cucumber defense mechanisms is called evisceration. They expel their internal organs onto the attacker. The sticky white filaments distract or scare away the predator. Sometimes, a simple disturbance or change in water temperature can trigger the sea cucumber’s defense system.

Some sea cucumber species expel toxins that poison attackers.

There are some species of sea cucumber that use toxins to defend themselves from threats. When they are attacked, they discharge long and fine strings called Cuvierian tubules. These entangle and sometimes even poison the predator.

6. The sea cucumber can regenerate their internal organs very quickly.

Expelling their guts is no big deal to the sea cucumber because they can regenerate them back within a couple of weeks. Sometimes, it takes only a couple of days. Although all animals have some sort of wound repair process, not all have the power of regeneration. The sea cucumber has special cells that allow it to heal and regenerate their organs.

7. Sea cucumbers do not have a brain.

Sea cucumbers don’t have a true brain. They don’t have a memory and also can’t feel fear. Instead of a brain, they have a nerve ring around the mouth. The neural tissue acts as its nervous system and controls how the sea cucumber operates or reacts to its surroundings. They also don’t have distinct sensory organs. But, all the nerve endings on their skin allow them to have a sense of touch and sensitivity to light.

Eyed Sea Cucumber (Bohadschia ocellata)
Image by Bernard DUPONT

8. One species of the sea cucumber can grow up to 10 feet.

There are over 1,700 species of sea cucumbers and they are very diverse. The average size of a sea cucumber is  4-12 inches. One species called the Synapta maculata can grow up to 10 feet. It is also known as the snake sea cucumber. This species is native to the tropical Indo-Pacific ocean.

A long thin holothurian sea cucumber
Image by David Burdick

The smallest sea cucumber measures only 2 centimeters.

The smallest ever sea cucumber can be found in Vizhinjam Bay in India. Scientists stumbled upon the species Thyonina bijui in 2015. The miniscule sea cucumber has a reddish brown body and grows up to only 2 centimeters.

9. Sea cucumbers eat through their retractable tentacles.

Sea cucumbers are scavengers. They spend most of their lives crawling on the sea bed looking for food. What do sea cucumber eat? Their diet consists mostly of algae, plankton and other debris. They get their food by using tentacles and eating sediments while crawling on the sea bed. Some species are floater feeders. Instead of crawling, they stay in one place and extend their tentacles upwards to catch floating plankton.

Sea cucumber
Image by Tenor

10. Sea cucumbers are considered a delicacy in some cultures.

Sea cucumbers are considered a delicacy in Asia, particularly in China. They are also believed to have medicinal benefits. In Chinese medicine, they are used to treat ailments like impotence, arthritis and cancer. Their supposed healing powers are the reason why sea cucumbers are so expensive. The most expensive sea cucumber is the Japanese sea cucumber, which costs up to $3,500 a kilo.

Eating sea cucumbers can be dangerous because of their toxins.

While most species are safe to eat, there are a few that are toxic to humans. There have been instances of humans having bad reactions from eating sea cucumbers. If not prepared correctly or if species get confused, poisoning can happen.

sea cucumber in hand
Image by Kindel Media

How endangered is this animal?

Humans have made a big business out of selling sea cucumbers. They are not just consumed as food, their nutrients are also extracted for skincare products. Commercial fishing and illegal poachers have been exploiting sea cucumbers for more profit and it is hurting the seas.

  • Some sea cucumber populations are shrinking because of overconsumption.
    Because of overfishing, some species of sea cucumber are shrinking. The soaring demand for the marine animal has resulted in dwindling populations in about 80 of its source countries. About 16 species have been listed as threatened and 7 are listed as already endangered.
  • Illegal poachers risk their lives to collect sea cucumbers to sell to the black market.
    Not only is the ecosystem negatively affected, human lives are at stake as well. Illegal fishermen dive for rare sea cucumbers without the proper gear and tools. Many have been injured and there have been several deaths reported too. Illegal poachers sell sea cucumbers to the black market for an expensive price.
  • Protecting Sea Cucumbers Will Keep Our Marine Ecosystem Balanced.
    This unhealthy overconsumption has negative effects on the ecosystem. Sea cucumbers are the “cleaners of the sea”. Without them, there will be an unbalance of nutrients in the waters. Coral reefs will also likely suffer. Ultimately, we need to protect sea cucumbers and develop more sustainable solutions to keep our marine ecosystem healthy and well-balanced.



Also Known As



Generally between 10 to 30 cm (4 to 12 in) in length


The Indian Ocean and the western Pacific


Deep seafloor


Plankton and decaying organic matter found in the sea


5 to 10 years

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