Sea cucumber facts for kids

Quick facts for kids Sea Cucumber
Scientific classification
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Holothuroidea

Sea cucumbers are a class of echinoderms, the Holothuroidea. They have a longish body, and leathery skin. Sea cucumbers live on the floor of the ocean. Most sea cucumbers are scavengers. There are about 1500 species of sea cucumbers. Sea cucumbers have a unique respiratory system, and effective defences against predators. The Chinese people eat them.

Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcareous structures that are usually reduced to isolated ossicles joined by connective tissue. These can sometimes be enlarged to flattened plates, forming an armour. In pelagic species the skeleton is absent.

Overview

Sea cucumber, Coconut Island, Hawaii

Sea cucumber in the Seychelles ejects sticky filaments in self-defense.

Sea cucumbers communicate with each other by sending hormone signals through the water.

A remarkable feature of these animals is the collagen which forms their body wall. This can be loosened and tightened at will. If the animal wants to squeeze through a small gap, it can undo the collagen connections, and pour into the space. To keep itself safe in these cracks, the sea cucumber hooks up all its collagen fibers to make its body firm again.

The animals have an internal respiratory tree which floats in the internal watery cavity. At the rear, water is pumped in and out of the cloaca, so gaseous exchange takes place with the respiratory tree in the gut.

Defense

Some species of coral reef sea cucumbers defend themselves by expelling sticky cuvierian tubules to entangle potential predators. These tubules are attached to the respiratory tree in the gut. When startled, these cucumbers may expel the tubules through a tear in the wall of the cloaca. In effect, this squirts sticky threads all over a predator. Replacement tubules grow back in one-and-a-half to five weeks, depending on the species. The release of these tubules can also be accompanied by the discharge of a toxic chemical known as holothurin, which has similar properties to soap. This chemical can kill any animal in the vicinity and is one more way in which these sedentary animals can defend themselves. Other cucumbers, lacking this device, can split their intestinal wall, and spew out their gut and respiratory tree. They regenerate them later. Zoologists who experience this believe it to be an impressive deterrent. "The mess one individual can make must be seen to be believed".

The existence of these defenses explains why the holothurians were able to do without the strong skeleton of their ancestors.

Feeding

Highly modified tube feet around the mouth are always present. These are branched and retractile tentacles, much larger than the regular tube feet. Sea cucumbers have between ten and thirty such tentacles, depending on the species. With their sticky tentacles the animal collects detritus and small organisms.

Images for kids

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  Thelenota ananas, a giant sea cucumber from the Indo-Pacific tropics

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  Sea cucumber : a -Tentacles, b - Cloaca, c - Ambulacral feet on the ventral side, d -Papillae on the back

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  A sea cucumber atop gravel, feeding

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  "Auricularia" larva (by Ernst Haeckel)

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  Emperor shrimp Periclimenes imperator on a Bohadschia ocellata sea cucumber

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  Tonna perdix, a selective predator of tropical sea cucumbers

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  Apodida like this Euapta godeffroyi are snake-shaped, without podia, and have pinnate tentacles.

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  Holothuriida like this Holothuria cinerascens are sausage-shaped, with peltate tentacles.

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  Dendrochirotida like this Cercodemas anceps are curled-bodied and have arborescent tentacles.

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  Elasipodida like this "sea pig" Scotoplanes have a translucent body with specific appendages; they live in the abyss.

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  Synallactida like this Stichopus herrmanni still lack a definition.

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  Dried sea cucumbers in a Japanese pharmacy

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  Holothurians plate by Ernst Haeckel from his Kunstformen der Natur (1904)

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  Details of the mouth with its tentacles.

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  Synaptula lamperti lives on sponges (here in Indonesia).

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  Synapta maculata, the longest known sea cucumber (Apodida).

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  The king sea cucumber (Thelenota anax, family Stichopodidae) is one of the heaviest known holothurians.

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  Chiridota heheva, abyssal species.

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  Cucumaria miniata, a filter-feeding sea cucumber.

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  Pseudocolochirus ("sea apple").

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  Holothuria leucospilota

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  Isostichopus badionotus

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  Thelenota rubralineata

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  Holothuria fuscopunctata

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  Bohadschia argus

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  The mouth of an Euapta godeffroyi, showing pinnate tentacles.

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  Mouth of a Holothuria sp., showing peltate tentacles.

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  Mouth of a Cucumaria miniata, with dendritic tentacles, for filtering the water.

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  Lissocarcinus orbicularis, a symbiotic crab.

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  Periclimenes imperator, a symbiotic shrimp.

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  Polynoid worms on a king sea cucumber.

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  "Teripang" in a market in Asia.

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  Sea cucumber in sauce in China.

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  Haisom cah jamur, Chinese Indonesian sea cucumber with mushroom.

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  Deep fried sea cucumbers.

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  Kripik teripang, Indonesian sea cucumber cracker.

See also

In Spanish: Pepinos de mar para niños