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 ?
Regeneration in the holothurian echinoderm Synaptula hydriformis Lesueur.
Hawkins, "Negligible recovery in Chagos holothurians (sea cucumbers)," Aquatic Conservation: Marine and Freshwater Ecosystems, vol.
On the seafloor there are many crabs (Cancer, Loxorhyncus), starfish (Pisaster, Patiria, Pycnopodia, Solaster), sea urchins (Strongylocentrotus), holothurians (Parastichopus, Cucumaria), and abalones (Haliotis).
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.
Like many other animals, holothurians are capable of replacing the cells that get lost or worn out in the course of normal functioning of the digestive tube.
Distribution and density of two holothurian species in Cubagua Island, Venezuela.
On the one hand, in some holothurians the intestine regenerates after evisceration as an outgrowth from remaining structures (esophagus and cloaca); that is, it demonstrates one feature of epimorphosis (growth from the wound surface).
Large echinoderm clades, such as most of the holothurians and possibly all of the living crinoids, have lecithotrophic larvae.
Gore & Abele (1976) reported this species associated with holothurians and among hidroids, but without indicating a clear commensal relationship.
Oocytes in holothurians, as in other echinoderms, are produced in the ovary of the female; they are formed from reproductive cells called germ cells, in a process referred to as oogenesis.