''Parakaryon myojinensis'', also known as the Myojin parakaryote, is a highly unusual species of single-celled organism known only from a single specimen, described in 2012. It has features of both prokaryotes and eukaryotes but is apparently distinct from either group, making it unique among organisms so far discovered. It is the sole species in the genus ''Parakaryon''.

Etymology

The generic name ''Parakaryon'' comes from Greek παρά (''pará'', "beside") and κάρυον (''káryon'', "kernel", "nucleus"), and reflects its distinction from eukaryotes and prokaryotes. The specific name ''myojinensis'' reflects the locality where the only sample was collected: from the bristle of a scale worm collected from hydrothermal vents at Myōjin Knoll (明神海丘, ), about deep in the Pacific Ocean, near

Aogashima is a volcanic island to the south of Japan in northernmost Micronesia. It is the southernmost and most isolated inhabited island of the Izus, which are politically and administratively part of Japan but geographically not part of the Japanes ...

island, southeast of the

Japanese archipelago The Japanese archipelago (Japanese: 日本列島, ''Nihon rettō'') is a group of 6,852 islands that form the country of Japan, as well as the Russian island of Sakhalin. It extends over from the Sea of Okhotsk in the northeast to the East Chin ...

Structure

''Parakaryon myojinensis'' has some structural features unique to eukaryotes, some features unique to prokaryotes, and some features different to both. The table below details these structures, with matching traits coloured beige.

Classification

It is not clear whether ''P. myojinensis'' can or should be classified as a eukaryote or a prokaryote, the two categories to which all other cellular life belongs. Excluding

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es, which are non-cellular and often distinguished from cellular life, and excluding several fossils that contain disputed evidence of ancient life (

nanobacteria ''Nanobacterium'' ( , pl. ''nanobacteria'' ) is the unit or member name of a former proposed class of living organisms, specifically cell-walled microorganisms, now discredited, with a size much smaller than the generally accepted lower limit ...

, nanobes), ''P. myojinensis'' is the only organism to have a completely unknown position in the

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. Adding to the difficulties of classification, only one instance of this organism has been discovered to date, and so scientists have been unable to study it further. British evolutionary biologist Nick Lane hypothesized in a 2015 book that the existence of ''P. myojinensis'' may be an important clue to the origins of life on Earth, perhaps as an example of the abiogenesis of simple organisms from organic compounds continuing in the present day. The fact that ''P. myojinensis'' was discovered near hydrothermal vents, which have been proposed as possible primordial reaction chambers for the earliest ancestors of prokaryotes and eukaryotes, lends credence to this idea.

Etymology

Structure

Classification

See also

References

Further reading