Marrus orthocanna – a deeper, darker, colder relative of the Portuguese man o’ war but with much less of a sting in its tail
Marrus orthocanna is a species of pelagic siphonophore, an organism comprised of a colony of individual animals (zooids) that work together in order to survive.
Belonging to the same phylum (Cnidaria) as coral, jellyfish and anemones, Marrus orthocanna is closely related to the Portuguese man o’ war, the jellyfish-like siphonophore famous for its blue bell and stinging tentacles. Unlike its more famous surface-swimming relative, however, M. orthocanna is a cold-water organism, most commonly encountered between 200m and 800m in cold Arctic water, including the northernmost reaches of the Pacific and Atlantic Oceans, the Bering Sea and, occasionally, the Mediterranean.
The small orange sac at the top of the thin, central ‘stalk’ of the organism’s body – in the top-right of the image above – is the pneumatophore, which keeps the animal buoyant – the equivalent to the man o’ war’s large blue float. The series of bell-shaped zooids attached to the stalk are nectophores which, like a series of coordinated jellyfish, expand and contract to provide locomotion.
The orange mass underneath is a collection of tentacles known as the siphosome, which can extend up to 50cm from the colony and reach up to 2m in length, although the body stalk with the nectophores is only around 10cm long.
The siphosome is a collection of polyps and stinging cells which provide food for the rest of the organism. After swimming into position using its nectophores, the siphosome is deployed like a large net curtain, trapping and paralysing small crustaceans as they pass by, which are then digested by other zooids within the structure.
Reproduction is asexual, and the entirety of the new organism is generated from a single fertilised egg. Each of the different zooids buds from the central stem as it lengthens, producing a collection of genetically identical workers, each with their own specialised tasks helping to keep the rest of the siphonophore alive.
More from DIVE’s Miscellany of Marine Curios:
- Marine Curios #12 – Clione limacina, or naked sea butterfly
- Marine Curios #11 – order Xiphosura, or horseshoe crabs
- Marine Curios #10 – Pseudocolochirus violaceus or sea apple
- Marine Curios #9 – Periophthalmus modestus or Shuttles hoppfish
- Marine Curios #8 – Grimothea planipes, or the pelagic or red or tuna crab (or langostilla)
- The complete collection of DIVE’s Miscellany of Marine Curios
