Parakaryon myojinensis
Drawing showing unique cell structure with cell wall, single nuclear membrane, and a single large spiral endosymbiont (seen in section), a combination found neither in prokaryotes nor eukaryotes. Cell is 10 μm long.
Scientific classification
Higher classification:incertae sedis
Genus:Parakaryon
Yamaguchi et al. 2012[1]
Species:P. myojinensis
Yamaguchi et al. 2012[1]
Parakaryon myojinensis
Location of Myōjin Knoll off the coast of Japan, where the specimen was found

Parakaryon myojinensis, also known as the Myojin parakaryote, is a highly unusual species of single-celled organism known 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.[1] 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,[2] 32°06.2′N, 139°52.1′E) 1240 m deep in the Pacific Ocean, near Aogashima island, SE of the Japanese archipelago.[1]

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.[1][3]

Structure Prokaryotes Eukaryotes Parakaryon myojinensis
Nucleus present No Yes Yes
No. of nuclear membrane layers N/A 2 1
Nuclear pores present N/A Yes No
Ribosome location Cytoplasmic Cytoplasmic Cytoplasmic and intranuclear
Endosymbionts present No Yes Yes
Endoplasmic reticulum present No Yes No
Golgi apparatus present No Yes No
Mitochondria present No Yes[note 1] No
Chromosome structure Variable Linear Filamentous
Cytoskeleton present Yes Yes No

Classification

It is not clear whether P. myojinensis can be classified as a eukaryote or a prokaryote, the two categories to which all other cellular life belongs. Excluding viruses, which are non-cellular and often distinguished from cellular life, and excluding several fossils that contain disputed evidence of ancient life (nanobacteria, nanobes), P. myojinensis is the only organism to have a completely unknown position in the tree of life.[citation needed] 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.[1][4]

See also

References

  1. ^ a b c d e f Yamaguchi M, Mori Y, Kozuka Y, Okada H, Uematsu K, Tame A, Furukawa H, Maruyama T, Worman CO, Yokoyama K (2012). "Prokaryote or eukaryote? A unique microorganism from the deep sea". J Electron Microsc (Tokyo). 61 (6): 423–431. doi:10.1093/jmicro/dfs062. PMID 23024290.
  2. ^ "Fumitoshi MURAKAMI, The Forming Mechanism of the Submarine Caldera on Myojin Knoll in the Northern Part of the Izu-Ogasawara (Bonin) Arc".
  3. ^ Evolution of complex life on Earth, take 2
  4. ^ Nick Lane (2015). "Epilogue: From the Deep". The Vital Question: Energy, Evolution, and the Origins of Complex Life. W.W.Norton and Company. pp. 281–290. ISBN 978-0-393-08881-6.

Further reading