Parakaryon myojinensis

Parakaryon myojinensis is a single-celled organism known by a unique example. "[T]his organism appears to be a life form distinct from prokaryotes and eukaryotes",^[1] with features of both.

Classification

It is not clear whether P. myojinensis can be classified as either a eukaryote or a prokaryote, the two kinds of organisms known so far.

• Eukaryotes are organisms with one or more complex cells which contain a nucleus. All plants, animals, fungi, etc. are composed of eukaryotic cells.
• Prokaryotes are simple cells without a nucleus: bacteria and archaea.

The newly discovered organism has a nucleus and other endosymbionts (organisms living within other cells), so would appear to be a eukaryote. However the nuclear membrane is a single layer, not a double layer as in other eukaryotes, and the DNA is stored in filaments as in bacteria, which are prokaryotes. So this organism has not been classified as either a eukaryote or a prokaryote.

Adding to the difficulties of classification, only one instance of this organism has been discovered to date. So scientists have not been able to observe it further.

Name

The generic name, Parakaryon comes from Greek παρα (next to) and [Eu]karyota and reflects its position between eu- and prokaryotes. The specific name, myojinensis reflects the locality where the samples have been collected: the hydrothermal vents at the Myōjin Knoll (明神海丘,^[2] 32°06.2′N, 139°52.1′E) off the coast of Japan at a depth of 1240 m.^[1]

References

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.
2. Fumitoshi MURAKAMI, The Forming Mechanism of the Submarine Caldera on Myojin Knoll in the Northern Part of the Izu-Ogasawara (Bonin) Arc

• 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.