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Sea Cucumbers  

Sea cucumbers are Echinoderms with a leathery skin and a sausage-shaped body. There are about 1,150 species of sea cucumbers. Theyare found in most oceans and at depths that range from the shallows to the deep sea lying directly on the bottom or burrowing through the sediments on the bottom.

Most sea cucumbers range in length from 10 to 30 centimetres although the smallest species is only 3 millimetres long and the largest can reach 100 cm in length. They do not have arms like many other Echinoderms but do have tube feet, often with suckers, that allow the animal to crawl.

They move using their tube feet. found on their lower surface, and rhythmic contractions of their fleshy bodies. Some deep sea species can swim. The outer body has a tough, leathery texture, although a few species have hardened regions of calcium carbonate for additional protection from predators. The head region is surrounded by a 10 to 30 feeding tentacles surrounding a simple mouth.

Diversity in Sea Cucumbers

Sea cucumbers extract oxygen from water using a pair of 'respiratory trees' near the anus. They 'breathe' by drawing water in through the anus and then expelling it.

Sea cucumbers are a very important part of marine food webs. Almost all sea cucumbers are detritivores eating tiny scraps of food that settle on the sea floor including invertebrates, algae, bacteria, and decaying organic matter. Some are "Direct deposit feeders” wiping their tentacles over the sediments to pick up tiny food particles that settle there from the water above. Others are "Suspension feeders" using special tentacles to pick particles out of the water.

Their predators include crabs, crustaceans, sea turtles, sea stars, fish and humans. Their tough skin is a protection against predators as is their burrowing behaviour and camouflage. They can also expel some of their internal organs to confuse predators. These organs can be regrown in a couple of months or less. Some also release a poison into the water to kill their predators.

In most sea cucumbers, the calcium carbonate plates are microscopic and are embedded beneath the skin. Their leathery skin is mainly made from collagen fibres, these fibres can be loosened and tightened to allow sea cucumbers to squeeze through small gaps as if it was liquefing its body.

Most sea cucumbers are either male or female and fertilization takes place outside of the body in the water. The fertilized eggs develop into free-living larvae that are dispersed with water currents and become part of the plankton. They eventually settle onto the sea floor and develop into adults.

Over 30 species of sea cucumber fertilise their eggs internally and a few species of cold-water sea cucumbers brood their larvae in special pouches on their body.

At depths below 8.8 km sea cucumbers are found in large herds that move across the ocean searching for food. They can also be found in great numbers in some shallow waters.

Sea cucumber
Image © Sabine Pennison

This sea cucumber's tentacles can be clearly seen
Image © Lisa York Flickr


Macro photo of a sea cucumber's skin
Image © Michael Fontenoti Flickr

Did you know?
In some parts of the world, especially Southeast Asia and China, sea cucumbers are considered a delicacy and are widely harvested as food. They are often dried to preserve them and are used as food and in herbal and pharmaceutical medicines. Recent increases in demand have had a significant impact on local populations of sea cucumbers, and overharvesting has resulted in the virtual disappearance of these animals from many areas.

Dried Sea cucumbers

Sea Cucumber expelling its intestines
As a defense mechanism a sea cucumber will shoot part of its respiratory
system out of its body when bothered. Fish will go after the guts and give
the cucumber time to scoot away and live another day.

Sea Cucumber
From Animal Planet



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