Siphonophorae

Taxobox
name = Siphonophores


image_width = 200px
image_caption = Portuguese Man o' War, "Physalia physalis" (Cystonectae: Physaliidae)
regnum = Animalia
subregnum = Eumetazoa
phylum = Cnidaria
subphylum = Medusozoa
classis = Hydrozoa
subclassis = Leptolinae
ordo = Siphonophorae
ordo_authority = Eschscholtz, 1829
subdivision_ranks = Suborders
subdivision =
Calycophorae

Cystonectae

Physonectae

synonyms =Siphonophora Eschscholtz, 1829

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 Siphonophoraa. The best known species is the dangerous Portuguese Man o' War ("Physalia physalis")

Description

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. [Dunn (2005)]

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"). [Haddock "et al." (2005)]

ystematics

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: [MarineSpecies.org (2008)]

Suborder Calycophorae
* Family Abylidae
* Family Clausophyidae
* Family Diphyidae
* Family Hippopodiidae
* Family Prayidae
* Family SphaeronectidaeSuborder Cystonectae
* Family Physaliidae
* Family RhizophysidaeSuborder Physonectae
* Family Agalmatidae
* Family Apolemiidae
* Family Athorybiidae
* Family Erennidae
* Family Forskaliidae
* Family Physophoridae
* Family Pyrostephidae
* Family Rhodaliidae

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

Haeckel's siphonophores

Ernst Haeckel described a number of siphonophores, and several plates from his "" (1904) depict members of the taxon:

Footnotes

References

* (2005): [http://siphonophores.org/SiphOrganization.php Siphonophores] . Retrieved 2008-JUL-08.
* (2005): Bioluminescent and red-fluorescent lures in a deep-sea siphonophore. "Science" 309(5732): 263. PMID 16002609 doi|10.1126/science.1110441 (HTML abstract)
* (2008): [http://www.marinespecies.org/aphia.php?p=taxdetails&id=13551 Anthomedusae] . Retrieved 2008-JUL-08.

External links

* http://www.ville-ge.ch/musinfo/mhng/hydrozoa/sipho/siphonophora.htm
* http://siphonophores.org