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Loricifera
Temporal range: Middle Cambrian–Recent[1] (total group)
Pliciloricus enigmaticus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
Superphylum: Ecdysozoa
Phylum: Loricifera
Kristensen, 1983[2]
Families

Loricifera (from Latin, lorica, corselet (armour) + ferre, to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals with 43 described species.[3] and approximately 100 more that have been collected and not yet described.[4] Their sizes range from 100 μm to ca.1 mm.[5]

They are characterised by a protective outer case called a lorica and their habitat is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by R.M. Kristensen, near Roscoff, France.[6] They are among the most recently discovered groups of animals.[7] They attach themselves quite firmly to the substrate, and hence remained undiscovered for so long.[8] The first specimen was collected in the 1970s, and described in 1983.[7] They are found at all depths, in different sediment types, and in all latitudes.[8]

Morphology

The animals have a head, mouth, and digestive system, as well as the lorica. The head (which contains the mouth and the brain), a trunk region surrounded by six plates that make up the 'lorica' or corselet and – in between these two – the neck region. Loricifera have a well developed brain and each scalid is individually connected to the brain by nerves. The armor-like lorica consists of a protective external shell or case of encircling plicae.[9] There is no circulatory system and no endocrine system. Many of the larvae are acoelomate, with some adults being pseudocoelomate, and some remaining acoelomate.[7] Development is generally direct, though there are so-called Higgins larvae, which differ from adults in several respects. As adults, the animals are gonochoric. Very complex and plastic life cycles of pliciloricids include also paedogenetic stages with different forms of parthenogenetic reproduction. Most Loricifera are dioecious, meaning there are males and females. However, there are a few species known to be hermaphroditic, which means they contain both male and female reproductive organs. [10] [4] Fossils have been dated to the late Cambrian.[11]

Taxonomic affinity

See also: List of bilateral animal orders

Morphological studies have traditionally placed the phylum in the Vinctiplicata with the Priapulida; this plus the Kinorhyncha constitutes the taxon Scalidophora. The three phyla share four characters in common – chitinous cuticle, rings of scalids on the introvert, flosculi, and two rings of introvert retracts.[6][7] However, despite a 2015 study showing the phylum's closest relatives being the Panarthropoda,[12] a 2022 study again showed that it belonged to the Scalidophora and told that further, more comprehensive genetic tests will be required to find its actual position in Ecdysozoa.[13]

Light microscopy image of Spinoloricus cinziae adapted to an anoxic environment (stained with Rose Bengal). Scale bar is 50 μm.

Evolutionary history

The loriciferans are believed to be miniaturized descendants of a larger organism, perhaps resembling the Cambrian fossil Sirilorica.[14] However, the fossil record of the microscopic non-mineralized group is (perhaps unsurprisingly) scarce, so it is difficult to trace out the evolutionary history of the phylum in any detail.

The 2017 discovery of the Cambrian Eolorica deadwoodensis may shed some light on the group's history.[15]

In anoxic environments

Three species of Loricifera have been found in the oxygen-free sediments at the bottom of the L'Atalante basin in Mediterranean Sea, more than 3,000 meters down, the first multicellular organisms known to spend their entire lives in an anoxic environment. Initially, it was thought that they are able to do this because their mitochondria act like hydrogenosomes, allowing them to respire anaerobically.[16][17] However, by 2021, questions arose as to whether or not they have mitochondria.[18]

The newly reported animals complete their life cycle in the total absence of light and oxygen, and they are less than a millimetre in size.[19] They were collected from a deep basin at the bottom of the Mediterranean Sea, where they inhabit a nearly salt-saturated brine that, because of its density (> 1.2 g/cm3), does not mix with the waters above.[19] As a consequence, this environment is completely anoxic and, due to the activity of sulfate reducers, contains sulphide at a concentration of 2.9 mM.[19] Despite such harsh conditions, this anoxic and sulphidic environment is teeming with microbial life, both chemosynthetic prokaryotes that are primary producers, and a broad diversity of eukaryotic heterotrophs at the next trophic level.[19]

Taxa


References

  1. ^ Peel, John S.; Stein, Martin; Kristensen, Reinhardt Møbjerg (9 August 2013). "Life Cycle and Morphology of a Cambrian Stem-Lineage Loriciferan". PLoS ONE. 8 (8): e73583. Bibcode:2013PLoSO...873583P. doi:10.1371/journal.pone.0073583. PMC 3749095. PMID 23991198.
  2. ^ Kristensen, R.M. (27 April 2009) [September 1983]. "Loricifera, a new phylum with Aschelminthes characters from the meiobenthos". Journal of Zoological Systematics and Evolutionary Research. 21 (3): 163–180. doi:10.1111/j.1439-0469.1983.tb00285.x. ISSN 0947-5745.
  3. ^ Cardoso Neves, Ricardo; Kristensen, Reinhardt Møbjerg; Møbjerg, Nadja (5 May 2021). "New records on the rich loriciferan fauna of Trezen ar Skoden (Roscoff, France): Description of two new species of Nanaloricus and the new genus Scutiloricus". PLOS ONE. 16 (5): e0250403. Bibcode:2021PLoSO..1650403N. doi:10.1371/journal.pone.0250403. PMC 8099068. PMID 33951070. id 10.1371.
  4. ^ a b Gad, Gunnar (17 June 2005). "Successive reduction of the last instar larva of Loricifera, as evidenced by two new species of Pliciloricus from the Great Meteor Seamount (Atlantic Ocean)". Zoologischer Anzeiger. 243 (4): 239–271. Bibcode:2005ZooAn.243..239G. doi:10.1016/j.jcz.2004.09.001.
  5. ^ Heiner, Iben (2005). "Preliminary account of the Loriciferan fauna of the Faroe Bank (NE Atlantic)". Annales Societatis Scientiatum Færoensis Supplementum. 41: 213–219. Archived from the original on 27 December 2016. Retrieved 26 December 2016.
  6. ^ a b Heiner, Iben; Kristensen, R.M. (18 March 2005). "Two new species of the genus Pliciloricus (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic". Zoologischer Anzeiger. 243 (3): 121–138. Bibcode:2005ZooAn.243..121H. doi:10.1016/j.jcz.2004.05.002.
  7. ^ a b c d Kristensen, R.M. (July 2002). "An introduction to Loricifera, Cycliophora, and Micrognathozoa". Integrative and Comparative Biology. 42 (3): 641–651. doi:10.1093/icb/42.3.641. PMID 21708760.
  8. ^ a b Ruppert, Edward E.; Fox, Richard S.; Barnes, Robert D., eds. (2004). Invertebrate Zoology (7th ed.). p. 776. ISBN 978-0-03-025982-1.
  9. ^ Heiner, Iben; Sorensen, Martin Vinther; Kristensen, Reinhardt Mobjerg (2004). "Loricifera (Girdle Wearers)". Grzimek's Animal Life Encyclopedia. Vol. 1. New York, NY: Van Nostrand Reinhold Company. pp. 343–350.
  10. ^ Schmidt-Rhaesa, Andreas (2013). Gastrotricha, Cycloneuralia, and Gnathifera. p. 362. ISBN 978-3-11-021938-8.
  11. ^ "Discovery of new fossil from half billion years ago sheds light on life on Earth: Scientists find 'unfossilizable' creature". Science Daily (Press release). January 2017.
  12. ^ Yamasaki, Hiroshi; Fujimoto, Shinta; Miyazaki, Katsumi (30 June 2015). "Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences". Zoological Letters. 1: 18. doi:10.1186/s40851-015-0017-0. ISSN 2056-306X. PMC 4657359. PMID 26605063.
  13. ^ Howard, R. J., Giacomelli, M., Lozano-Fernandez, J., Edgecombe, G. D., Fleming, J. F., Kristensen, R. M., Ma, X., Olesen, J., Sørensen, M. V., Thomsen, P. F., Wills, M. A., Donoghue, P. C., & Pisani, D. (2022). The Ediacaran origin of ecdysozoa: Integrating fossil and Phylogenomic Data. Journal of the Geological Society, 179 (4). https://doi.org/10.1144/jgs2021-107
  14. ^ Peel, John S. (March 2010). "A corset-like fossil from the Cambrian Sirius Passet lagerstätte of North Greenland and its implications for cycloneuralian evolution". Journal of Paleontology. 84 (2): 332–340. Bibcode:2010JPal...84..332P. doi:10.1666/09-102R.1. JSTOR 40605520. S2CID 86256781.
  15. ^ Harvey, Thomas H.P.; Butterfield, Nicholas J. (30 January 2017). "Exceptionally preserved Cambrian loriciferans and the early animal invasion of the meiobenthos" (PDF). Nature Ecology and Evolution. 1 (3): 0022. Bibcode:2017NatEE...1...22H. doi:10.1038/s41559-016-0022. hdl:2381/38658. PMID 28812727. S2CID 22874770. Archived (PDF) from the original on 9 October 2022.
  16. ^ Fang, Janet (8 April 2010). "Animals thrive without oxygen at sea bottom". Nature. 464 (7290): 825. Bibcode:2010Natur.464..825F. doi:10.1038/464825b. PMID 20376121. S2CID 4340458.
  17. ^ Milius, Susan (9 April 2010). "Briny deep basin may be home to animals thriving without oxygen". Science News.
  18. ^ Snyder, Alison (6 May 2021). "Something wondrous". Axios Science.
  19. ^ a b c d Mentel, Marek; Martin, William (6 April 2010). "Anaerobic animals from an ancient, anoxic ecological niche". BMC Biology. 8: 32. doi:10.1186/1741-7007-8-32. PMC 2859860. PMID 20370917.
  20. ^ Fujimoto, Shinta; Yamasaki, Hiroshi; Kimura, Taeko; Ohtsuka, Susumu; Kristensen, Reinhardt Møbjerg (14 November 2020). "A new genus and species of Loricifera (Nanaloricida: Pliciloricidae) from the deep waters of Japan". Marine Biodiversity. 50 (6): 103. Bibcode:2020MarBd..50..103F. doi:10.1007/s12526-020-01130-3. S2CID 228866331.

Further reading

Data related to Loricifera at Wikispecies