Parakaryon myojinensis

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.

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
Yamaguchi et al. 2012[1]
Species:P. myojinensis
Yamaguchi et al. 2012[1]
Location of Myōjin Knoll off the coast of Japan, where the specimen was found


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; the 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 and 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. Like eukaryotes and unlike prokaryotes, P. myojinensis has a nucleus and endosymbionts. However, the nuclear membrane is a single layer, not a double layer as in eukaryotes, and the DNA is stored in filaments rather than linear chromosomes. Furthermore, there is no endoplasmic reticulum, Golgi apparatus, cytoskeleton, mitochondria, or nuclear pores. Ribosomes are found not only in the cytoplasm but also in the nucleus. Adding to the difficulties of classification, only one instance of this organism has been discovered to date, and so scientists have not been able to study it further.[3][1][4]

See also


  1. 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. 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.
  4. Evolution of complex life on Earth, take 2

Further reading

  • Yamaguchi M, Yamada H, Uematsu K, Horinouchi Y, Chibana H (2018). "Electron Microscopy and Structome Analysis of Unique Amorphous Bacteria from the Deep Sea in Japan". Cytologia. 83: 336–341. doi:10.1508/cytologia.83.337.CS1 maint: multiple names: authors list (link)
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.