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The 'sea cucumber' is an echinoderm of the class 'Holothuroidea', with an elongated body and leathery skin, which is found on the sea floor worldwide. It is so named because of its cucumber-like shape.
Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, but this can actually be absent in some species.

Contents

Overview

Sea cucumbers as food and medicine

Sea cucumbers in art

See also

Notes

External links

Overview

Sea cucumbers are generally scavengers, feeding on debris in the benthic layer. (There are only a few exceptions to this, most notably a few pelagic cucumbers and the species Rynkatropa pawsoni, which has a commensal relationship with deep-sea angler fish.^[1]) The diet of most cucumbers consists of plankton and decaying organic matter found in the sea. One way they might get a supply of food is to position themselves in a current where they can catch food that flow by with their tentacles when they open. Another way is to sift through the bottom sediments using their tentacles. They can be found in great numbers beneath fish farms.
Some species in the family Holothuriidae (coral-reef sea cucumbers) within the order Aspidochirotida can defend themselves by expelling sticky tubules that entangle potential predators. Cuvierian tubules are enlargements of the respiratory tree that float freely in the coelom. When startled, a sea cucumber that possesses these tubules can expel some of them through a tear in the wall of the cloaca; this process is called eversion. The sea cucumber does not expel all of the tubules at one time. Replacement tubules grow back in one-and-a-half to five weeks , depending on the species.[1]
They can be found in great numbers on the deep sea floor, where they often make up the majority of the animal biomass ([2] and [3]).
The body of deep water holothurians is made of a tough gelatinous tissue with unique properties that makes the animals able to control their own buoyancy, making it possible for them to both living on the ocean floor or floating over it to move to new locations with a minimum of energy.[4]
Also in more shallow waters they can form dense populations. The strawberry sea cucumber (Squamocnus brevidentis) of New Zealand, lives on rocky walls around the southern coast of the South Island where the number are something reaching densities of 1,000 animals in a square metre. For this reason, one such area in Fiordland is simply called the strawberry fields.[5]
Sea cucumbers extract oxygen from water in a pair of 'lungs' or respiratory 'trees' that branch off the cloaca just inside the anus, so that they 'breathe' by drawing water in through the anus and then expelling it.^[2][3] A variety of fishes, most commonly pearl fishes, have evolved a commensalistic symbiotic relationship with sea cucumbers in which the pearl fish will live in sea cucumber's cloaca using it for protection from predation, a source of food (the nutrients passing in and out of the anus from the water), and to develop into their adult stage of life. Many polychaete worms and crabs have also specialized to use the cloacal respiratory trees for protection by living inside the sea cucumber.^[4]
Sea cucumbers reproduce by releasing sperm and ova into the ocean water. Depending on conditions, one organism can produce thousands of gametes.
The largest American species is ''Holothuria floridana'', which abounds just below low-water mark on the Florida reefs.
The most common way to separate the subclasses is by looking at their oral tentacles. Subclass Dendrochirotacea has 8-30 oral tentacles, subclass Aspidochirotacea has 10-30 leaflike or shieldlike oral tentacles, while subclass Apodacea may have up to 25 simple or pinnate oral tentacles and is also characterized by reduced or absent tube feet, as in the order Apodida.

Sea cucumbers as food and medicine

Sea cucumber is considered a delicacy in Far East countries such as Malaysia, Singapore,China, Japan, Korea, and Indonesia as well as in certain Mediterranean countries such as Spain. It is also highly valued for its supposed medicinal properties. The flesh of the animal is "cleaned" in a process that takes several days. The food item is often purchased dried, and then rehydrated before use. The product is used in soups, stews and braised dishes due to its gelatinous texture. In most Chinese speaking regions, when used as an ingredient or a dish, it is called by its Cantonese name, ''hoi sam''. In Japanese cuisine, Konowata is made of sea cucumber entrails which are extracted, salted, and cured.
To supply the markets of Southern China, Macassan trepangers traded with the Indigenous Australians of Arnhem Land. This Macassan contact with Australia is the first recorded example of trade between the inhabitants of the Australian continent and their Asian neighbours.
Some varieties of sea cucumber (known as ''gamat'' in Malaysia or ''trepang'' in Indonesia) are said to have excellent healing properties. There are pharmaceutical companies being built based on this gamat product. Extracts are prepared and made into oil, cream or cosmetics. Some products are intended to be taken internally. The effectiveness of sea cucumber extract in tissue repair has been the subject of serious study^[5]. It not only helps a wound heal more quickly but is also said to reduce scarring.^[6].

Sea cucumbers in art

Sea cucumbers have inspired musical composition: in the first of his ''Embryons desséchés'' for piano solo, Erik Satie presents the "(Desiccated embryo) of a Holothurian" and inserts a description of the animal in the score:
:The Holothurian crawls across boulders and rocky surfaces.
:This sea-animal purrs like a cat; also, it produces disgusting silky threads.
:Light appears to have an incommodating effect on it.
Nonetheless it is the sea cucumber's closest relative (the echinoidea or sea urchin) that gets the most attention from scientists, both as an embryo and as a fossil.
Sea cucumbers have also inspired thousands of haiku in Japan, where they are called "namako" (ナマコ), written with characters that can be translated "sea mice". In English translations of these haiku, they are usually called "sea slugs"; there is a book with almost 1000 holothurian haiku translated from Japanese titled "Rise, Ye Sea Slugs!" by Robin D. Gill (ISBN 0-9742618-0-7). According to the Oxford English Dictionary, the "sea slug" is a holothurian first, but biologists insist on using "sea slug" only for the nudibranch, a marine-dwelling relative of land slugs.

See also

★ Trepanging

★ Gamat

Notes

1. Brusca, R.C., Brusca, G.J.; ''Invertebrates''. Sinauer Associates, Massachusetts, 1990.
2. Holothurians or sea cucumbers (describes breathing processes)
3. Cool as a Sea Cucumber - URL retrieved august 19, 2005
4. Aquarium Invertebrates by Rob Toonen, Ph.D.
5. Study of healing properties (PDF format)
6. Effects on tissue repair

External links

★

★ Healing properties of the gamat

★ Chek Jawa Link for more photos of sea cucumber and more.

★ Traditional Chinese dish of braised duck with sea cucumber

★ Images of Sea cucumbers