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(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.



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.


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Zhizn’ zhivotnvkh, vol. 1. Moscow, 1968.
Dogel’. V. A. Zoologiia bespozvonochnykh, 6th ed. Moscow, 1975.

A. V. IVANOV [23–1436–]

References in periodicals archive ?
DEEP FEEDING: Gelatinous siphonophores (top), which may be Earth's most abundant predators, capture fish and other prey by unfurling curtains of stinging tentacles; thin as a broomstick, the largest grow longer than blue whales.
Epipelagic siphonophore assemblages associated with water masses along a transect between Chile and Easter Island (eastern South Pacific Ocean).
This organization was very reminiscent of that in the two siphonophores and of that reported for another hydroid, Coryne (Golz, 1994).
The behavior of ascidian sperm is quite different from that in the siphonophore sperm.
In fact, many systematic descriptions of hydromedusae and siphonophores during the past 200 years were based only on fragments of animals (e.
Siphonophores follow a similar pattern with the exception of neustonic species (e.
The calycophoran siphonophore Hippopodius hippopus is normally transparent, but rapidly becomes opaque when disturbed, presumably as a defense response (Mackie, 1996).
Luminescent bacteria, sponges, anemones and corals, siphonophores, jellyfish, mollusks, crustaceans, and echinoderms are covered.
The ship also discovered new siphonophores - huge colonies of tiny organisms that gang together and specialise so that they appear to be a single complex animal - the Portugese Man of War is the best known example and some of the colonies can grow to over 50 metres long.
The mesopelagic fauna also includes many kinds of squid, krill, and siphonophores and ctenophores (jellyfish-like animals), as well as worms, sea butterflies, and larvae that comprise the DSL zooplankton.