Sea Cucumber, a marine animal, shaped like a cucumber or sausage, related to the starfish and the sea urchin. There are more than 500 species, found in shallow and deep waters throughout the world. Depending on species, sea cucumbers range in length from about one inch to six feet (2.5 to 180 cm). A common North American and European species is about 10 inches (25 cm) long.

Sea cucumbers are usually black, brown, or olive green. They have bumpy, leathery skin, embedded with bony particles. Some-sea cucumbers have tiny tube feet along the length of their body. (Tube feet are hollow, muscular projections that are used in locomotion.) Those species that lack tube feet creep about the sea floor by muscular movements of the body. Some sea cucumbers hide in grassy beds and others burrow in mud and sand. At one end of the body is a mouth surrounded by 10 to 30 food-gathering tentacles. The sea cucumber feeds on tiny marine animals and other organic matter.

When disturbed by an enemy such as a fish or a crab, the sea cucumber will often eject long, sticky threads from its body to entangle its enemy. Some species of sea cucumbers will, at such times, violently contract their bodies and cast out a large part of their internal organs. The internal organs contain a toxin that is deadly to fish and other marine animals (but not to humans). These organs grow back in about six weeks.

The sea cucumber is considered a food delicacy and is used in soups by many Asian peoples. It is usually dried and then sold in markets, where it is known as trepang and also as beche-de-mer.

Which Echinoderms Eat Mud?

Mud is not something you'd ever want to eat. But it's the perfect meal for many sea cucumbers. As these echinoderms burrow along the ocean bottom, they open their mouths and take in the mud. The mud moves through the sea cucumber's body. As it does, tiny particles of dead organisms are separated out and used as food. The mud and the waste from digested food continue on through and go out the other end of the sea cucumber's body.

Unlike other echinoderms, most sea cucumbers have tube feet that look like tentacles. These tentacles are located around the animal's mouth.

Sea cucumbers that eat mud use their tentacles to burrow through and push mud into their bodies. Those that don't eat mud use their tentacles to catch plankton. After sea cucumbers catch food this way, they stuff their tentacles into their mouths. They wipe food particles off inside their mouths when they pull their tentacles out.

How Does a Sea Cucumber Protect Itself?

When a sea cucumber is threatened, it may shoot sticky threads from its waste hole. Enemies, such as fish and crabs, may get caught in the threads. That's enough to send most predators elsewhere to look for food. The sea cucumber can grow a new set of threads and do this trick again and again.

Some sea cucumbers can spew out their digestive systems and grow them back again. Scientists don't believe they do this to scare predators, though. They probably do this to protect themselves from building up too much waste in their bodies.

The sea cucumber's body is shaped much like the vegetable it's named after. Most of the body is soft and squishy. But below the skin, a sea cucumber does have spiny plates. These are so small and far below the skin that they can't be seen.

Which Sea Cucumbers Are Also Called Sea Apples?

Some sea cucumbers are commonly called sea apples. That's because they are round like apples instead of long and slender like cucumbers. Many of these striking echinoderms are found near coral reefs. There, these brightly colored sea cucumbers use their tube feet to slowly crawl about. When in danger, sea apples can pull their short tentacles back into their bodies for protection.

Like all sea cucumbers, sea apples have holes in their bodies to expel waste. But not all echinoderms have these openings. Some sea stars and brittle stars do not. Scientists think these echinoderms get rid of waste through their skin or tube feet.

Sea cucumbers form the class Holothuroidea. A common North American and European species is Cucumaria frondosa.