Siphonophore

Marrus orthocanna is a species of pelagic siphonophore, a colonial animal. It has zooids, some of which are polyps and some medusae.
It lives in the Arctic and other cold, deep waters, swimming independently in mid-ocean.

The Siphonophores are an order of cnidarian invertebrates in the class Hydrozoa. The Portuguese man o' war is an example.

A siphonophore is not a single animal. It is a colony of four kinds of zooids. Zooids are very small, highly modified individuals. All the zooids in a colony are genetically identical. These zooids are specialized polyps and medusoids.

Though structurally similar to other cnidarians, the zooids do not live by themselves: they are attached to each other. Each type of zooid is not self-sufficient. It depends for survival on the others doing what it cannot do by itself.

So close do the zooids fit together that the colony looks like a single individual. It was a triumph of 19th century biology to discover the real nature of the siphonophores.

• Bathyphysa conifera
• Portuguese man o' war

Siphonophore Media

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  Portuguese man o' war (Physalia physalis)

• Video taken at a depth of 612 metres of the siphonophore Nanomia bijuga
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  • (top center): Epibulia Ritteriana (Haeckel) = Epibulia ritteriana Haeckel, 1888?, mature colony * (bottom right): Cystalia monogastrica (Haeckel) = Epibulia ritteriana H
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  • (center): Discolabe quadrigata (Haeckel) = Physophora hydrostatica Forskål, 1775, colony * (top left): Discolabe quadrigata (Haeckel) = Physophora hydrostatica Forskål, 1775, gas bladder and bells from above * (top right): Discolabe quadrigata (Haeckel) = Physophora hydrostatica
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  See full-size image for index to numbers. * "Strobalia cupola" (Haeckel) = Forskalia sp.?, colony * "Strobalia cupola" (Haeckel) = Forskalia sp.?, gas bladder from above * "Strobalia cupola" (Haeckel) = Forskalia sp.?, polyp/medusae cluster with all but the feeding apparatus and cover removed * "Strobalia cupola" (Haeckel) = Forska

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  • (center): Praya galea (Haeckel) = Rosacea cymbiformis (delle Chiaje, 1830), colony * (top left): Praya galea (Haeckel) = Rosacea cymbiformis (delle Chiaje, 1830)