Holothurians

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Holothurians

 

(sea cucumbers), a class of invertebrates (Holothurioidea) of phylum Echinodermata.

The skeleton of the holothurians is greatly reduced. The body is pentactinally symmetrical, which is characteristic of the phylum in general, but in the holothurians it is marked by the biliterally symmetrical arrangement of many of the organs. The largest holothurians reach 2 m in length. The body is vermiform, with a mouth at one end and an anal opening at the other. The mouth, surrounded by a crown of tentacles that serve to capture the food, leads into a long tubular gut. Respiration is accomplished by an ambulacral system and a so-called respiratory tree—branched sacs leading to the rectum. Holothurians develop by metamorphosis; free-swimming larvae hatch from the eggs. There are some 1,100 species.

The holothurians are exclusively marine, benthic, sluggish, creeping animals, feeding on sediment or tiny plankton. When greatly irritated they are capable of self-mutilation (au-totomy), but the lost organs readily regenerate. In China the sea cucumber is dried and used as food. The animals (particularly the trepang) are also of some commercial importance in the USSR, in the Far East.

REFERENCES

Dogel’, V. A. Zoologiia bespozvonochnykh, 5th ed. Moscow, 1959.
Bol’shoi praktikum po zoologii bespozvonochnykh, part 2. Moscow, 1946.
Zhizn’ zhivotnykh, vol. 2. Moscow, 1968.
References in periodicals archive ?
Tropical fisheries are traditionally based on several holothurians (Fig.
The fishery research institutes of India (Central Marine Fisheries Research Institute) and Sri Lanka (National Aquatic Research Agency) have been conducting studies on the biology of several commercial holothurians and have evaluated the resources for many years.
Mariculture of Stichopus japonicus has started in Hokkaido and involves hatchery production of juveniles which are transplanted to fishing grounds From the 1990 statistics, Japanese imports of holothurians are low, with frozen products at 115 t and dried products at 18 t.
Information on recruitment, growth, and mortality of holothurians is only available for a few species (Shelley, 1985; Conand, 1989b), and research on these subjects should be given priority.
Some additions to our knowledge of the New Zealand holothurians.
Synchronous gamete maturation and reliable spawning induction method in holothurians.
Two new rhabdocoel turbellarians parasitic in Tasmanian holothurians.