Sea cucumbers are among the most bizarre looking creatures in the ocean. They are truly unique, not just in appearance, but also in their structure. They are echinoderms and they cover the sea beds worldwide. One of the most numerous of the sea animals, they are found in the shallows and also at great depths. Eyeless creatures, elongated in their shape and possessing leathery skin, they don't much resemble the animals that we know. They lack the bilateral symmetry of the majority of the creatures of the animal kingdom. Their bodies have five distinct sections instead of a left and a right. They are aptly named because most of them are close in appearance to a cucumber, they move almost imperceptibly slowly. They could easily be mistaken for a plant. Many are harvested and eaten throughout the world. But more important than their contribution to feeding the people in many countries, they provide a service for the ocean by filtering the water of bacteria, plankton and plant debris. Many species use their tentacles to draw food into their mouths as they slowly move over the ocean floor. Like millions of small ocean "Roombas", they work constantly, ridding the reefs, rocks, and sand bottoms of decaying plant matter. Without them, many animals would suffer from habitat loss. Algae that provide food could not grow and the silt and debris would simply accumulate and clog corals. Scuba divers enter the ocean with a sense of wonder for the incredible abundance of life that exists below the waves. The plants and animals there are unlike anything that we see above the surface. This undersea domain is alien and beautiful and each trip to the depths is an ad venture beyond description.