Marrus orthocanna is a species of pelagic siphonophore,[2][3] a colonial animal composed of a complex arrangement of zooids, some of which are polyps and some medusae.

[6] Like other siphonophores, Marrus orthocanna is a colony composed of a number of specialised zooids linked together by a long stem.

[7] At the front is the pneumatophore, an orange-colored, gas-filled float, the largest of which can reach estimated sizes of 5-10 centimeters in diameter [8].

[10] At these depths the temperature is about 4 °C (39 °F), hardly any light penetrates from the surface and human observation is limited to what can be seen from submersible craft.

[15] Marrus orthocanna can reach lengths of 2-3 meters long and the tentacles can extend fifty centimeters on either side.

[16] It moves forward intermittently before pausing to put out its "fishing lines", ready to ensnare passing creatures.

It is a carnivore whose diet is thought to consist mainly of small crustaceans such as decapods, krill, copepods and mysids.

Another growth zone sees the development of the siphosome and the continuing elongation of the stem carries these zooids down with it.

[9] The division of labor among the zooids is an evolutionary advance in the constant struggle for existence in the deep sea.

[19] Marrus orthocanna itself was discovered by Paul Lassenius Kramp as part of the Godthaab Expedition of 1928, as they explored the area to the west of Greenland looking specifically at phytoplankton.