Siphonophora

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Siphonophora

[‚sī·fə′näf·rə]
(invertebrate zoology)
An order of the cnidarian class Hydrozoa characterized by the complex organization of components which may be connected by a stemlike region or may be more closely united into a compact organism.

Siphonophora

 

a subclass or, according to another taxo-nomic system, an order of free-swimming marine coelenterates of the class Hydrozoa. The body, which ranges in length from 1 cm to 3 m, is generally colorless and transparent. Only a few species are brightly colored. Siphonophorans form polymorphic colonies whose individuals, polyps and medusae, differ in structure and are converted into organs of the colony. At the apex there is usually a swim bladder, or pneumatophore, with gas, chiefly nitrogen, which is released by the gas gland to help keep the colony vertical. In some siphonophorans, for example, the Physalia, the pneumatophore emerges at the surface of the water and functions as a sail. A colony also consists of nectocalyxes (swimming bells), which are modified medusae whose contractions propel the colony, and feeding polyps (gas-trozooids), which swallow and digest prey and bear a long tentacle (lasso cell) with a group of stinging cells. There also are sexual individuals (gonozooids). Heterogenous members of the colony are usually gathered in aggregates called cormidia. Siphonophorans reproduce sexually; the free-swimming larva, a modified planula, forms a new colony by budding.

Siphonophorans of the order Disconanta are not colonies but solitary free-swimming polyps. Of the 250 species, most inhabit tropical seas. Only two species, one from each of the genera Dimophyes and Physophora, are found in the USSR. Some large tropical siphonophorans, for example, the Portuguese man-of-war (Physalia), are dangerous to man; prolonged contact with the long (up to 10 m) tentacles in water causes severe burns and systemic disease with protracted elevation of body temperature.

REFERENCES

Dogel’, V. A. “Tip kishechnopolostnykh.” In Rukovodstvo po zoologii, vol. 1. Moscow-Leningrad, 1937. Pages 323-30.
Zhizn’ zhivotnvkh, vol. 1. Moscow, 1968.
Dogel’. V. A. Zoologiia bespozvonochnykh, 6th ed. Moscow, 1975.

A. V. IVANOV [23–1436–]

References in periodicals archive ?
The positive correlation of nitrites, nitrates, phosphates and silicates with zooplankton biomass, and nitrate+nitrite with cladocerans, medusae and siphonophores leads us to suggest that upwelled waters could favor the abundance of these groups through primary production enhancement.
siphonophores: sea creatures with clear, filmy bodies and stinging cells that band together in floating colonies.
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Siphonophores have gas-filled spheres in the upper zooid of the colony that maintain them permanently and almost effortlessly in suspension.
Laurence Madin, a transplanted fourth generation Californian, makes his home in Massachusetts studying gelatinous an reals such as medusae, siphonophores, ctenophores, and pelagic tunicares.
The coastal convergence that separates the cold waters of the platform from the deep and less cold waters marks the limit of the distribution of the oceanic species, mainly copepods with circumpolar distribution and with a remarkable abundance of gelatinous species of zooplankton, such as medusas, siphonophores, salps, and sea butterflies (pteropod mollusks).
The expedition also provided specimens that resulted in publications on sea birds, siphonophores, isopods, and echinoderms, as well as other invertebrate taxa (Table 2).
Horizontal and vertical distributions of siphonophores in relation to oceanographic conditions in Chilean Patagonian fjords.
Strategies for sperm chemotaxis in the siphonophores and ascidians: a numerical simulation study.
The latest creatures to enter the red zone are siphonophores of the genus Erenna.
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