Plectus parvus
{{short description|Species of freshwater and terrestrial roundworm}}
{{Taxobox
| image =
| image_caption =
| regnum = Animalia
| phylum = Nematoda
| classis = Chromadorea
| ordo = Plectida
| familia = Plectidae
| genus = Plectus
| species = P. parvus
| binomial = Plectus parvus
| binomial_authority = Bastian, 1865{{cite web|url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=229346|title=WoRMS – World Register of Marine Species – Plectus parvus Bastian, 1865|website=Marinespecies.org|access-date=1 September 2018}}
| subdivision_ranks =
| subdivision =
}}
Plectus parvus is a species of nematode (roundworm) found in freshwater and terrestrial environments. It has been sampled in Europe and New Zealand. Along with the similar nematode Panagrolaimus detritophagus, in 2018 it was the first species of multicellular eukaryote to be thawed into a living state after prolonged cryopreservation. Female worms of this species were found in Pleistocene permafrost in the Kolyma River lowland (one of the sites was near the Alazeya River).{{cite web|url=https://www.atlasobscura.com/articles/siberian-worms-revived|title=Siberian Worms Survived More Than 30,000 Years Stuck in Permafrost|date=30 July 2018|publisher=Atlas Obscura|access-date=1 September 2018}} They were mobile and ate, after being frozen for 30–40 thousand years.{{cite web |url=https://www.livescience.com/63187-siberian-permafrost-worms-revive.html |title=Worms Frozen for 42,000 Years in Siberian Permafrost Wriggle to Life |author=Weisberger, Mindy |date=27 July 2018 |publisher=Live Science |access-date=8 September 2018}}{{cite journal|title=Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland|first1=A. V.|last1=Shatilovich|first2=A. V.|last2=Tchesunov|first3=T. V.|last3=Neretina|first4=I. P.|last4=Grabarnik|first5=S. V.|last5=Gubin|first6=T. A.|last6=Vishnivetskaya|first7=T. C.|last7=Onstott|first8=E. M.|last8=Rivkina|date=1 May 2018|journal=Doklady Biological Sciences|volume=480|issue=1|pages=100–102|doi=10.1134/s0012496618030079|pmid = 30009350}}
Taxonomy
Plectus parvus was described by the English zoologist Henry Charlton Bastian in 1865. The names Plectus potamogeti (Schneider, 1937) and Rhabdolaimus baltonicus (Daaday, 1894) are considered synonyms.{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=59872#null|title=ITIS Standard Report Page: Plectus parvus|website=Itis.gov|access-date=1 September 2018}} Sources differ on its higher level taxonomy. The World Register of Marine Species places it in order Plectida, while the Integrated Taxonomic Information System places it in the order Araeolaimida.
Anatomy
Adults of this species are reported to grow to 0.4–0.6 mm long.{{cite web|url=https://nematode.unl.edu/pleparv.htm|title=Plectus parvus|first=Peter|last=Mullin|website=Nematode.unl.edu|access-date=1 September 2018}} They possess two alae. The body is defended by a thin cuticle. The males possess asymmetrical spicules.
Ecology
In the river sediments and soils it inhabits, this worm is part of the benthos group. It has been shown that interaction between this species and another soil nematode Bursilla monhysteria in damp podzols increases both bacterial biomass and nitrogen mineralisation.{{cite book|author=Sparks, Donald L.|title=Advances in Agronomy|url=https://books.google.com/books?id=aIwUb7UVKLkC&pg=PA65 |year=2011 |publisher=Academic Press |isbn=978-0-12-385538-1 |page=65}} It is one of the nematodes present in estuarine mud, and because of the absence of quantifiable levels of megafauna present in more polluted sediments, these nematodes can be used to assess pollution levels.{{cite journal |author=Zullini, A. |year=1976 |title=Nematodes as indicators of river pollution |journal=Nematologia Mediterranea |volume=4 |issue=1 |url=http://journals.fcla.edu/nemamedi/article/view/85187 }}
References
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