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. It is the sole species in the genus Parakaryon.
|Higher classification:||incertae sedis|
Yamaguchi et al. 2012
Yamaguchi et al. 2012
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, 32°06.2′N, 139°52.1′E) 1240 m deep in the Pacific Ocean, near Aogashima island, SE of the Japanese archipelago.
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.
- Anatoma fujikurai, a species of gastropod discovered at the same location
- 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.
- "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.
- Evolution of complex life on Earth, take 2