''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 A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

and

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

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 vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

s 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

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...

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 ...

nanobe A nanobe () is a tiny filamental structure first found in some rocks and sediments. Some scientists hypothesize that nanobes are the smallest form of life, 1/10 the size of the smallest known bacteria. No conclusive evidence exists that th ...

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

tree of life The tree of life is a fundamental archetype in many of the world's mythological, religious, and philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The Assyrian Sacred Tree: A History ...

. 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 Nick Lane (born 1967) is a British biochemist and writer. He is a professor in evolutionary biochemistry at University College London. He has published five books to date which have won several awards. Career Educated at Imperial College, Lon ...

hypothesized in a 2015 book that the existence of ''P. myojinensis'' may be an important clue to the

origins of life In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothes ...

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