Holothurians


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Related to Holothurians: Holothuroidea, Sea cucumbers

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 ?
Hemolytic activities of triterpene glycosides from the holothurian order Dendrochirotida: some trends in the evolution of this group of toxins.
Recruitment in the Holothurian Cucumaria frondosa in the Gulf of Maine.
Asexual reproduction, evisceration and regeneration in holothurians.
Under the crowded mass of leaves one may see larger sessile organisms on the rhizomes, similar to those of the rocky floor, and on the sediment sea urchins rest while holothurians ceaselessly gobble the sand for its food content.
Conservation of aspidochirotid holothurians in the littoral waters of Kenya.
During the different stages of the processing (boiling, gutting, drying), the length and weight of the holothurians are greatly reduced, resulting in the final product weighing about 10% of the original weight and measuring 50% or less of the original length.
Sea cucumbers, or holothurians, are exclusively marine invertebrates classified in the phylum Echinodermata, class Holothuroidea.
Gore & Abele (1976) reported this species associated with holothurians and among hidroids, but without indicating a clear commensal relationship.
For example, the intestine of holothurians can regenerate in five different ways, and within a single species the regeneration of the intestine varies according to the stage of the life cycle and the method of wounding (Dolmatov, 2009).