The Sea Cucumber Eats, Poops and Breathes Through a Cloaca

Would you eat this? Comstock Images / Getty Images

The soft, cylindrical sea cucumber looks like a vegetable — and in some countries, it's a delicacy because of its nutritional value and health benefits. But it actually belongs to the phylum of echinoderms, closely related to starfish (aka sea stars), sand dollars, sea urchins and sea lilies.

Many sea cucumber species can be found in a variety of habitats, from shallow coral reefs to the deep sea. They are especially abundant in the Indo-Pacific region, but they also inhabit cold waters in the Arctic and Antarctic.

These animals also play a vital role in oceans around the world, keeping the seafloor clean.

Physical Characteristics

Sea cucumbers come in a variety of shapes, sizes and colors. These squishy marine animals can be as small as 2 to 3 inches (7 centimeters), whereas other sea cucumbers can grow to over 6 feet (1.8 meters) long.

Most sea cucumbers are shaped like an elongated cucumber with leathery skin covered in tiny bumps. Sea cucumbers have five rows of tube feet that are powered by a water vascular system, allowing them to move across the ocean floor and grasp objects by controlling water pressure within their feet.

On one end of the body, you'll find the sea cucumber's mouth, surrounded by tentacle-like structures used for feeding.

A starfish clings to a sea cucumber underwater — A large sunflower star attempts to prey upon a sea cucumber, which struggles to wiggle out of its captors arms.
Stuart Westmorland / Getty Images

The other end, the anus (or cloaca), expels waste, but has other purposes as well. Sea cucumber can breathe through their cloaca by pumping water in and out of it. The pumping of water can also help them swim better. They can also eat with their cloacas.

The cloacas can help them defend against predators. Sometimes their cloacas have teeth. Other times, sea cucumbers can tear a hole in its own interior wall and shoot out a tangle of Cuvierian tubules at their predators. It looks like they are trapping their enemies with sticky spider webs.

And lastly, sea cucumbers can eject their internal organs through their cloacas, which scares potential predators. These organs are regenerated in a few days inside the sea cucumber. (Sounds like a complicated digestive system.)

Sea Cucumber Subspecies

There are over 1,200 known species of sea cucumbers, each with its own unique characteristics. Some, like the black sea cucumber (Holothuria atra), are common in tropical waters, while others, such as the giant red sea cucumber (Parastichopus californicus), can be found in colder, temperate regions.

The enormous Synapta maculata is the species that can be over 6 feet (1.8 meters) long. Despite their differences, all sea cucumbers share the same basic structure and ecological role as cleaners of the deep seafloor.

Solitary Echinoderms

Sea cucumbers are generally solitary creatures, spending most of their time crawling along the seafloor in search of food. However, during spawning seasons, they gather in large groups to release eggs and sperm into the water for external fertilization.

Life Cycle

The life cycle of a sea cucumber begins when eggs and sperm are released into the water, where fertilization occurs. The resulting larvae drift in the ocean as plankton before settling on the seafloor and developing into juveniles.

They can live for several years, depending on the species and environmental conditions.

What Do Sea Cucumbers Eat?

The sea cucumber is a detritivore, meaning it feeds on decomposing organic matter and microorganisms found in the sediment. Using its tentacle-like structures, a sea cucumber scoops up sand and mud, digesting the nutritious particles and expelling the rest.

This diet might sound unappetizing, but it's essential for maintaining healthy marine ecosystems.

Environmental Impact

Sea cucumbers help keep the oceans clean by eating fish waste and debris. They process large amounts of sediment and recycle it back into the environment. They even improve sediment quality, as the sand they excrete is cleaner than the sand they eat.

Their excretions fertilize the surrounding areas, provide nutrients for coral growth and help buffer against ocean acidification.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.