''Mertensia ovum'', also known as the Arctic comb jelly or sea nut, is a

cydippid Cydippida is an order of comb jellies. They are distinguished from other comb jellies by their spherical or oval bodies, and the fact their tentacles are branched, and can be retracted into pouches on either side of the pharynx. The order is not ...

comb jelly Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ...

ctenophore Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ...

first described as ''Beroe ovum'' by Johan Christian Fabricius in 1780. It is the only species in the genus ''Mertensia''. Unusually among ctenophores, which normally prefer warmer waters, it is found in the Arctic and adjacent polar seas, mostly in surface waters down to . In addition to being weakly

bioluminescent Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...

in blues and greens, comb jellies produce a rainbow effect similar to that seen on an oil slick, and which is caused by interference of incident light on the eight rows of moving

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

or comb rows which propel the organism. The comb rows beat sequentially, rather like the action of a Mexican wave. The comb rows also function as chemical sense organs, serving the same role as insect antennae. ''Mertensia ovum'' is the major source of bioluminescence from Arctic gelatinous zooplankton. This species, like other ctenophores, has a large body cavity and is carnivorous, feeding on

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s and small crustaceans snagged by its two extremely sticky and robust tentacles (see Tentaculata). These are long and contractile with numerous lateral tentillae or side branches bearing

colloblasts Colloblasts are unique, multicellular structures found in ctenophores. They are widespread in the tentacles of these animals and are used to capture prey. Colloblasts consist of a collocyte containing a coiled spiral filament, internal granules and ...

, each of which consists of a coiled spiral filament, structurally similar to a

nematocyst A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

, but instead of injecting a toxin, release an adhesive substance which ensnares the prey. These tentacles can be retracted into a tentacle sheath. The body is on the whole light pink in colour, oval in the tentacular plane and considerably compressed in the sagittal plane. Its unconventional brain consists of a network of nerves arranged under its outer skin. A study in the Barents Sea found that it ingests prey ranging from small copepods to amphipods and krill, but that its staple diet consists of large copepod species such as '' Calanus finmarchicus'', ''

Calanus glacialis ''Calanus glacialis'' is an Arctic copepod found in the north-western Atlantic Ocean, adjoining waters, and the northwestern Pacific and its nearby waters. It ranges from sea level to in depth. Females generally range from about in length, an ...

'', ''

Calanus hyperboreus ''Calanus hyperboreus'' is a copepod found in the Arctic and northern Atlantic. It occurs from the surface to depths of . Description The size of ''C. hyperboreus'' varies with its geography; individuals located in more temperate waters usually ...

'' and '' Metridia longa''. Like garden snails, ''Mertensia'' is hermaphroditic, reproducing sexually and occasionally asexually. Eggs and sperm are ejected into the water and from the fertilized eggs ovoid larvae develop. The planktonic larvae of this species are long while adults grow up to . The genus ''Mertensia'' commemorates the German naturalist Karl Heinrich Mertens aka Andrei Karlovich Mertens (17 May 1796 – 18 September 1830). Mertens accompanied the Russian naturalist Alexander Philipov Postels aboard the ''Senyavin'' in 1826 on a voyage to ''"reconnoitre and describe the coasts of Kamchatka, the land of the Chuchkis and the Koriaks (the coasts of which have not yet been described by anyone, and which are unknown except by the voyage of Captain Bering); the coasts of the Okhotsk Sea, and the

Shantar Islands The Shantar Islands (russian: Шантарские острова, translit=Shantarskiye ostrova) are a group of fifteen islands located off the northwestern shore of the Sea of Okhotsk east of Uda Gulf and north of Academy Bay. Most of the isla ...

, which although they are known to us, have not been sufficiently described."''

References

External links

* * {{Taxonbar, from1=Q641104, from2=Q21442318 Tentaculata Bioluminescent ctenophores Animals described in 1780 Taxa named by Johan Christian Fabricius