Siphonophora


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Related to Siphonophora: order Siphonophora

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 ?
A Synopsis of the Siphonophora. British Museum, London.
Sifonoforos (Coelentetata: Siphonophora) de las costas de Quintana Roo.
Nuevos registros y ampliacion de ambito de especies de Siphonophora (Cnidaria) en aguas del Atlantico mexicano.
Gelatinous zooplankton assemblages associated with water masses in the Humboldt Current System and potential predatory impact by Bassia bassensis (Siphonophora: Calycophorae).
Se identificaron los siguientes grupos del holozooplancton: radiolarios (Clase Radiolaria), foraminiferos (Orden Foraminifera), sifonoforos (Orden Siphonophora), medusas (Clase Hydrozoa excepto sifonoforos), clenoforos (Phylum Ctenophora), tecosornados (Orden Thecosomata), gimnosomados (Orden Gymnosomata), heteropodos (Suborden Heteropoda), poliquetos (Clase Polychaeta), cladoceros (Orden Cladocera), ostracodos (Subclase Ostracoda), copepodos (Subclase Copepoda), misidaceos (Orden Mysidacea), anfipodos (Orden Amphipoda), eufausidos (Orden Euphausiacea), decapodos pelagicos (Orden Decapoda), quetognatos (Phyllum Chaetognata), apendicularias (Orden Appendicularia) y tunicados (Clase Thaliacea).