It crawls along soft bottoms near coral reefs and seagrass beds ingesting sand and mud in its path. It separates out and digests any plant or animal matter and passes the sand, leaving a trail of clean sand behind. Meet the Sea Cucumber!
One of the most surprising things about sea cucumbers may be that they are animals, not plants.
Sea cucumbers live in a wide range of habitats, from shallow coastal areas to the deep sea. They are found in oceans around the world.
Although they don't look like it, sea cucumbers are related to sea stars, sea urchins, and sand dollars. This means they are echinoderms. Most echinoderms have visible spines, but the spines of a sea cucumber are tiny ossicles embedded in their skin. For some sea cucumber species, the tiny ossicles provide the only visible clue to the species' identity. The shape and size of these ossicles are examined under a microscope because they are so small.
There are some 1,250 known species, and many of these animals are indeed shaped like soft-bodied cucumbers.
Like other echinoderms, sea cucumbers have a water vascular system. The water vascular system of sea cucumbers is filled with body fluid rather than seawater.
These animals aren’t the best hunters in the seven seas, preferring to scavenge their food rather than track it down.
Sea cucumbers feed on tiny particles like algae, minute aquatic animals, or waste materials, which they gather in with 8 to 30 tube feet that look like tentacles surrounding their mouths. The animals break down these particles into even smaller pieces, which become fodder for bacteria, and thus recycle them back into the ocean ecosystem. Earthworms perform a similar function in terrestrial ecosystems.
Some species ingest sediment, remove the food particles and then excrete the sediment in long strands. One sea cucumber can filter up to 99 pounds of sediment in a year. The excretions of sea cucumbers help keep nutrients cycling throughout the ocean ecosystem.
Although they have some rows of tube feet, sea cucumbers move very slowly, if at all.
Sea cucumbers breathe through a respiratory tree that is connected to their anus.
The respiratory tree lies inside the body on either side of the intestine and connects to the cloaca. The sea cucumber breathes by drawing oxygenated water in through the anus. The water goes into the respiratory tree and oxygen is transferred into the fluids within the body cavity.
Sea cucumbers are nocturnal, meaning they are active during the night.
These echinoderms have an elaborate defensive system. This includes releasing dense and sticky white filaments to entangle any would-be predator or expelling internal organs, which are then regenerated. Some also produce holothurin, a toxin lethal to many fishes.
Pearlfish — and other small animals — have been known to take advantage of the sea cucumber, using its rectum as a sanctuary from predators. Sometimes it’s a commensal relationship because the cucumber is not harmed, but some pearlfish behave parasitically, feasting on some of its internal body parts.
There Are Male and Female Sea Cucumbers.
In most species of sea cucumbers, there are both males and females, although differences aren't externally visible. Many species reproduce by spawning — broadcasting their sperm and eggs into the water column. There, the eggs are fertilized and become swimming larvae that later settle to the ocean bottom.
Sea cucumbers, particularly eggs and young larvae, are prey for fish and other marine animals.
Sea Cucumbers Are Edible.
Sea cucumbers are harvested for use in food and medicine. Sea cucumbers have catch connective tissue, which seems to magically go from being stiff to flexible in mere seconds. This aspect of the sea cucumber is being studied for its potential application to the health and repair of human tendons and ligaments.
These animals are considered a delicacy in some areas and are especially popular in Asian countries. However, the unregulated harvest of sea cucumbers has caused a decline in some areas.
Although most sea cucumbers are harmless to humans, you should avoid picking them up as doing so may harm them or cause them to become disoriented.
