Mertensia ovum (lat.) Is a species of ctenophore from the order Cydippida (Cydippida), isolated into the monotypic genus Mertensia [1] . Unlike most ctenophore, Mertensia ovum - cold-water organisms, common in the seas of the Arctic Ocean , where they are confined to surface waters (usually no deeper than 50 m) [2] . At the end of the 20th century, the species was found in the Baltic Sea; some Baltic populations are represented exclusively by larvae less than 2 mm long, breeding pedogenetically [3] .
| Mertensia ovum |
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| Scientific classification |
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| Rod: | Mertensia Lesson , 1830 |
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| International Scientific Name |
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Mertensia ovum ( Fabricius , 1780) |
| Synonyms |
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- according to WoRMS [1] :
- Beroe ovum Fabricius, 1780
- Cydippe ovum Fabr. Mörch.
- Mertensia cucullus L. Agassiz , 1860
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Photo of
Mertensia ovum . One can see the iridescent refraction of light by rowing plates, as well as asynchronous contraction of tentacles
The species was first described in 1780 by the Danish zoologist Johann Fabrizius , who included it in the collective genus Beroe . The generic name Mertensia in 1830 was used by the French zoologist Rene Lesson in the name of the new ctenophore Mertensia groenlandica . In his publication, Lesson does not make a diagnosis of the species, citing the earlier work of Karl Mertens and William Scoresby [4] . Apparently, the generic name was formed from the name of Karl Mertens.
View of an individual taken in the plane of the pharynx
Adults Mertensia ovum reach a length of 55 mm [2] . The body has an ovoid shape, strongly flattened in the plane of the pharynx [2] . They have a pair of relatively massive tentacles, the length of which in the expanded state can be 20 times longer than the body [2] [5] . Numerous branches of tentacles (tentills) carry weapons from the colloblast cells used to catch prey. Movement in the water column is carried out due to the beating of the rowing plates - unique formations for ctenophorers, arisen on the basis of cilia and ordered in 8 rows; in Mertensia ovum, the rows of plates adjacent to the tentacles are longer [2] .
The body of Mertensia ovum is transparent; tentacles, rows of rowing plates, aboral field, and sex products have a pink hue [2] . Ctenophores of this species are capable of producing luminescent blue or green light and, apparently, are the most widespread form of bioluminescent organisms in the zooplankton of the Arctic seas [6] .
Mertensia ovum - hermaphrodites with external fertilization, oval larvae less than 2 mm long hatch from eggs. In arctic waters, the life cycle is 2 years or more. Direct observation of these ctenophores is difficult, but studies of the mass fraction of lipids indicate that the breeding season lasts from May to August [7] . Pedogenetic populations have been identified in the Baltic Sea, which are supported exclusively by reproduction in the larval stages [3] .
Like most tentacle ctenophores, Mertensia ovum are predators that feed on small plankton organisms. Their diet is represented primarily by copepods , but they also eat legumes of crayfish , pteropods of the Limacina genus (“sea devils”) and fish larvae [7] [8] . The proportion of representatives of this species in the biomass of jelly-like zooplankton can reach up to 70% [7] .
