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Siphonophora

(Order)

Overview

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Siphonophorae or Siphonophora, the siphonophores, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. The best known species is the dangerous Portuguese Man o' War (Physalia physalis). With a body length of 40?50 m, another species of siphonophore, Praya dubia, is one of the longest animals in the world.1]

Description

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Siphonophores are especially scientifically interesting because they are composed of medusoid and polypoid zooids that are morphologically and functionally specialized. Each zooid is an individual, but their integration with each other is so strong that the colony attains the character of one large organism. Indeed, most of the zooids are so specialized that they lack the ability to survive on their own. Siphonophorae thus exist at the boundary between colonial and complex multicellular organisms. Also, because multicellular organisms have cells which, like zooids, are specialized and interdependent, siphonophores may provide clues regarding their evolution.[1]

Like other hydrozoans, certain siphonophores can emit light. A siphonophore of the genus Erenna has been discovered at a depth of around 1,600 meters off the coast of Monterey, California. The individuals from these colonies are strung together like a feather boa. They prey on small animals using stinging cells. Among the stinging cells are stalks with red glowing ends. The tips twitch back and forth creating a twinkling effect. It is theorized that twinkling red light attracts small fish that have been found eaten by these siphonophores. While many sea animals produce blue and green bioluminescence, this siphonophore was only the second lifeform found to produce a red light (the first being the scaleless dragonfish Chirostomias pliopterus).[2]

Systematics

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Aspects of Physophora hydrostatica (Physonectae: Physophoridae).
Plate 37 in Kunstformen der Natur by Ernst Haeckel (1904). See also below.

Due to their highly specialized colonies, siphonophores have long misled scientists. They were for a long time believed to be a highly distinct group, but now are known to have evolved from simpler colonial hydrozoans similar to Anthomedusae or Leptomedusae. Consequently, they are now united with these in a subclass Leptolinae.

The Siphonophorae have long fascinated scientists and layfolk alike, due to their dramatic appearance as well as the large size and dangerous sting of several species. Compared to their relatives, their systematics are relatively straightforward:[3]

Suborder Calycophorae

Suborder Cystonectae

Suborder Physonectae

The genus Stepanyantsia is of unclear affiliations; it might belong in the Agalmatidae.

Footnotes

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  1. ^ a b Dunn (2005)
  2. ^ Haddock et al. (2005)
  3. ^ MarineSpecies.org (2008)
b>Siphonophorae or Siphonophora, the siphonophores, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. The best known species is the dangerous Portuguese Man o' War (Physalia physalis). With a body length of 40?50 m, another species of siphonophore, Praya dubia, is one of the longest animals in the world.1]

Description

[ Back to top ]

Siphonophores are especially scientifically interesting because they are composed of medusoid and polypoid zooids that are morphologically and functionally specialized. Each zooid is an individual, but their integration with each other is so strong that the colony attains the character of one large organism. Indeed, most of the zooids are so specialized that they lack the ability to survive on their own. Siphonophorae thus exist at the boundary between colonial and complex multicellular organisms. Also, because multicellular organisms have cells which, like zooids, are specialized and interdependent, siphonophores may provide clues regarding their evolution.[1]

Like other hydrozoans, certain siphonophores can emit light. A siphonophore of the genus Erenna has been discovered at a depth of around 1,600 meters off the coast of Monterey, California. The individuals from these colonies are strung together like a feather boa. They prey on small animals using stinging cells. Among the stinging cells are stalks with red glowing ends. The tips twitch back and forth creating a twinkling effect. It is theorized that twinkling red light attracts small fish that have been found eaten by these siphonophores. While many sea animals produce blue and green bioluminescence, this siphonophore was only the second lifeform found to produce a red light (the first being the scaleless dragonfish Chirostomias pliopterus).[2]

Systematics

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Aspects of Physophora hydrostatica (Physonectae: Physophoridae).
Plate 37 in Kunstformen der Natur by Ernst Haeckel (1904). See also below.

Due to their highly specialized colonies, siphonophores have long misled scientists. They were for a long time believed to be a highly distinct group, but now are known to have evolved from simpler colonial hydrozoans similar to Anthomedusae or Leptomedusae. Consequently, they are now united with these in a subclass Leptolinae.

The Siphonophorae have long fascinated scientists and layfolk alike, due to their dramatic appearance as well as the large size and dangerous sting of several species. Compared to their relatives, their systematics are relatively straightforward:[3]

Suborder Calycophorae

Suborder Cystonectae

Suborder Physonectae

The genus Stepanyantsia is of unclear affiliations; it might belong in the Agalmatidae.

Footnotes

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  1. ^ a b Dunn (2005)
  2. ^ Haddock et al. (2005)
  3. ^ MarineSpecies.org (2008)

References

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External links

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Taxonomy

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The Order Siphonophora is further organized into finer groupings including:

Families

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Abylidae

Abylidae is a family of marine invertebrates in the order Siphonophora. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. [more]

Agalmidae

[more]

Apolemidae

[more]

Apolemiidae

[more]

Athorybiidae

[more]

Clausophyidae

[more]

Codonidae

[more]

Diphyidae

[more]

Forskaliidae

[more]

Hippopodiidae

[more]

Physaliidae

Physalia is a genus of the order Siphonophora, colonies of four specialized polyps and medusoids that drift on the surface of the Atlantic, Indian and Pacific oceans. A gas-filled bladder resembling a blue bottle provides buoyancy, and long tentacles of venomous [nematocyst]s provide a means of capturing prey. A sail on the float, which may be left or right-handed, allows the wind to propel Physalia about the sea, often in groups. Individuals sometimes become stranded on beaches, where their toxic nematocysts can remain potent for weeks or months in moist conditions. [more]

Physophoridae

[more]

Prayidae

Prayidae is a family of marine invertebrates in the order Siphonophora. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. [more]

Pyrostephidae

[more]

Rhizophysidae

[more]

Rhodaliidae

[more]

Sphaeronectidae

[more]

At least 5 species and subspecies belong to the Family Sphaeronectidae.

More info about the Family Sphaeronectidae may be found here.

References

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External links

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Footnotes

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  1. ^ PinkTentacle.com (2008)
  2. ^ Dunn (2005)
  3. ^ Haddock et al. (2005)
  4. ^ MarineSpecies.org (2008)

Sources

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Last Revised: August 24, 2012
2012/08/24 13:14:58