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What is a Sea Cucumber?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

A sea cucumber is an echinoderm in the class Holothuroidea that can be found in all of the oceans of the world at depths ranging from the inter-tidal zone to the bottom of oceanic trenches. There are over 1,000 species of Holothurians, although all of them have the long cucumber-shaped bodies that give the animals their common name. Like other echinoderms, sea cucumbers display five sided radial symmetry along the length of their bodies. The rather bizarre ocean creatures are also prized in some Asian culinary traditions.

From a distance, one could be forgiven for mistaking a sea cucumber for an actual cucumber. Most of the time, the animals rest on the ocean floor, filtering food from the water that flows around them. Their dark, knobbly bodies do strongly resemble cucumbers, although some exotic species give away their animal nature with warts in colors like orange and blue. They eat plankton and other organic material, either through filter feeding or by sifting through the sediment on the ocean floor with the flexible tentacles that surround their mouths.

Sea cucumbers can be found in all of the oceans of the world.
Sea cucumbers can be found in all of the oceans of the world.

Like other ocean-going animals, the sea cucumber filters out oxygen from seawater to breathe. In this case, an apparatus to extract oxygen — called a breathing tree — starts at the base of the anus and runs along the animal's body. The cucumber intakes small amounts of water through the anus and cloaca, and then expels the waste back through the cloaca. The animal's simple breathing and digestive system suggests that it has been around for millions of years, and there are fossilized examples to support this hypothesis from the Silurian period, 400 million years ago.

Sea cucumber is popular in Asian cuisine.
Sea cucumber is popular in Asian cuisine.

Some species in this class do have a trick up their sleeve when self-defense is needed. Under moderate amounts of stress, one will squirt water from both ends. Under extreme stress, however, the animal will regurgitate its stomach and escape in the subsequent chaos. The stomach will regrow within a relatively brief period of time. Other echinoderms are also able to force their stomachs inside out, usually to feed, but the stomach usually retracts back into the body.

In Asian cuisine, sea cucumber appears both fresh and dried, and it is commonly used in soups and stews. The flavor is bland, and the texture is rubbery and slightly gelatinous. The animal is also used in some traditional medicines, and Western pharmaceutical companies have begun to study it to see if it contains useful properties. Some species appear to have anticoagulant, anti-inflammatory, and antimicrobial compounds that may be usable in medical treatment.

Frequently Asked Questions

What exactly is a sea cucumber?

A sea cucumber is an echinoderm, closely related to sea stars and sea urchins. These marine animals are named for their elongated body shape that resembles a cucumber. They play a vital role in ocean ecosystems by recycling nutrients as they feed on detritus and other organic matter on the sea floor.

How do sea cucumbers contribute to their ecosystem?

Sea cucumbers are essential for the health of marine ecosystems. They act as natural recyclers, breaking down detritus and other organic matter, which helps to prevent the accumulation of waste on the ocean floor. Their feeding process also helps to aerate the sediment, which is beneficial for other marine organisms.

Can sea cucumbers defend themselves, and if so, how?

Yes, sea cucumbers have unique defense mechanisms. When threatened, some species can expel sticky threads to entangle predators or release their internal organs, which are toxic to predators and can regenerate over time. This process, known as evisceration, is a remarkable survival strategy.

What do sea cucumbers eat and how do they feed?

Sea cucumbers are detritivores, meaning they consume decomposing organic matter and microorganisms. They feed by using their tentacle-like structures around their mouths to capture food particles from the sea floor or water column. This feeding process helps to keep ocean beds clean and nutrient-rich.

Are sea cucumbers important to humans?

Sea cucumbers are indeed important to humans. They are considered a delicacy in many cultures, particularly in Asia, and are harvested for food. Additionally, they are used in traditional medicine and are being researched for potential pharmaceutical applications due to their bioactive compounds.

How many species of sea cucumbers exist, and where can they be found?

There are over 1,250 known species of sea cucumbers, according to the World Register of Marine Species. They can be found in virtually all marine environments, from shallow coastal waters to the deep sea, and are particularly diverse in the Asia-Pacific region.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

GlassAxe

@ Anon73328- Sea cucumbers have both bilateral and radial symmetry. Sea cucumbers are purely pentaradial in symmetry during the larvae stage, but as the sea cucumber matures, it evolves a bilateral symmetry that is secondary to their pentaradial symmetry.

To understand this, think of the sea cucumber like a five-armed starfish. The anus of a sea cucumber is on one end of the animal, while the mouth is on the other. In between the mouth and the anus are five separate strips of flesh that make up the dermal layer of the sea cucumber. If you imagined those strips as unconnected, you could stand the creature up on its mouth, push the mouth and anus together, and you would have an animal with an anatomy similar to a starfish.

The adult sea cucumber spends its life lying horizontally, so it has developed a bilateral symmetry. If you cut the creature in half from mouth to anus the creature would be bilaterally symmetrical. That was tough to articulate, but I hope it helps.

anon73328

I am curious how you would respond to those sites that indicate that sea cucumbers have bilateral symmetry. My students and I are in "discussion" regarding the symmetry. I was taught that the sea cucumber has 5 parts, therefore radial symmetry. Can anyone help solve this?

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    • Sea cucumbers can be found in all of the oceans of the world.
      By: randimal
      Sea cucumbers can be found in all of the oceans of the world.
    • Sea cucumber is popular in Asian cuisine.
      By: xin wang
      Sea cucumber is popular in Asian cuisine.