Origin
Sea cucumbers are echinoderms of the Holothuroidea class. They are marine animals with a tanned skin and an elongated body with a single gonad.
They are found at the bottom of the seas and oceans all over the world. There are a number of species that are sought by humans for consumption.
Like all echinoderms sea cucumbers have a bony skeleton under the skin and a calcareous ring. In some species the calcareous ring and skeleton is missing.
Feeding sea cucumber
Sea cucumbers are generally scavengers, feeding on debris from other animals. The diet also contains plankton and decomposing organic matter.
Some species position themselves in water currents and fish for food with their tentacles. Many species possess the esophagus and stomach. The intestine is long and coiled.
Appearance sea cucumber
Sea cucumbers are usually between 10 and 30cm long. The smallest sea cucumber is only 3mm, and the largest can reach 1m.
Their bodies vary from nearly spherical to worm-like, and unlike other echinoderms, they have no defensive weapons. At one end is the mouth while at the other end is the anus.
A remarkable feature of these animals is the collagen that forms the wall of the body. They can creep in taking different forms due to this performance of being able to liquefy.
To be safe, they keep their body tough at all times. They can be found in large numbers on deep water bottoms. At depths greater than 9km sea cucumbers make up 90% of the macrofauna.
Their body is made of a hard gelatinous tissue with unique properties, which allows them to live at such great depths.
Sea cucumbers have no brains. A neural ring surrounds the oral cavity and sends nerves to the tentacles and pharynx. The animal is able to live if the nerve ring is surgically removed, demonstrating that it has no vital role in the Coordination of the nervous system.
Most species do not have distinct sensory organs, although there are various nerve endings scattered through the skin that give the animal a sense of touch and a sensitivity to light. Sea cucumbers extract oxygen from the water from the respiratory shafts that are inside the anus, so they breathe by drawing water through the anus, extracting oxygen, then expelling the water.
Like all echinoderms sea cucumbers possess both a vascularized water system that provides hydraulic pressure to the tentacles and tube feet, allowing them to move, and a network of veins through which blood circulates. Like all echinoderms they have pentaradial symmetry.
Behavior sea cucumber
Sea cucumbers communicate with each other by sending signals through the water. When needed, when frightened or attacked, some species release toxic chemicals.
This way of defending these toxic chemicals similar to soap can kill any animal nearby. In shallower waters sea cucumbers form dense populations.
The strawberry sea cucumber (brevidentis Squamocnus) of New Zealand lives on the rocky walls of the South Island where the population often reaches densities of 1000 animals per square meter. For this reason such an area is called simply Strawberry Field.
Breeding sea cucumber
Most sea cucumbers multiply by releasing sperm and eggs into the ocean. Depending on the conditions, an organism can produce thousands of gametes. The reproductive system consists of a single gonad.
At least 30 species fertilize eggs internally. The egg is then inserted into a bag in the adult's body. It gives birth through a tear in the wall near the anus. In other species the egg develops freely swimming in the form of larva 2-3 days having a length of only 1mm.
Indigenous Australians traded in markets in southern China for sea cucumbers. This contact is the first example of trade recorded between the inhabitants of the australian continent and the inhabitants of the Asian continent.
There are numerous species of sea cucumbers that are harvested and dried for export for use in Chinese cuisine. Some sea cucumbers are said to have healing properties.
