Loricifera

Loricifera (from Latin, lorica, corselet (armour) + ferre, to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals with 37 described species, in nine genera.[3][4][5] Aside from these described species, there are approximately 100 more that have been collected and not yet described.[4] Their sizes range from 100 µm to ca. 1 mm.[6] They are characterised by a protective outer case called a lorica and their habitat, which is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by Reinhardt Kristensen, in Roscoff, France.[7] They are among the most recently discovered groups of Metazoans.[8] They attach themselves quite firmly to the substrate, and hence remained undiscovered for so long.[5] The first specimen was collected in the 1970s, and later described in 1983.[8] They are found at all depths, in different sediment types, and in all latitudes.[5]

Loricifera
Temporal range: Middle Cambrian–Recent[1]
(total group)
Pliciloricus enigmatus
Pliciloricus enigmaticus
Scientific classification
Kingdom: Animalia
Phylum: Loricifera
Kristensen, 1983[2]
Order: Nanaloricida
Kristensen, 1983[2]
Families

Morphology

The animals have a head, mouth and digestive system as well as a lorica. 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.[8] Development is generally direct, though there are so-called Higgins larvae, which differ from adults in several respects. The animals have two sexes as adults. Very complex and plastic life cycles of pliciloricids include also paedogenetic stages with different forms of parthenogenetic reproduction.[4] Fossils have been dated to the late Cambrian[10].

Taxonomic affinity

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.[7][8] However, mounting molecular evidence indicates a closer relationship with the Panarthropoda.[11]

Spinoloricus
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.[12] However, the fossil record of the microscopic non-mineralized group is (perhaps unsurprisingly) scarce, so it is difficult to trace out the phylum's evolutionary history in any detail. The 2017 discovery of Cambrian Period Eolorica deadwoodensis may shed some light on the group's history.[13]

In anoxic environment

Three species of Loricifera have been found in the 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 oxygen-free environment. They are able to do this because their mitochondria act like hydrogenosomes, allowing them to respire anaerobically.[14][15]

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.[16] 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.[16] 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.[16] 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.[16]

Species

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. ^ a b Kristensen, R. M. (September 1983) [2009-04-27]. "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 – via Wiley Online Library.
  3. ^ Neves, Ricardo Cardoso; Reichert, Heinrich; Sørensen, Martin Vinther; Kristensen, Reinhardt Møbjerg (November 2016). "Systematics of phylum Loricifera: Identification keys of families, genera and species". Zoologischer Anzeiger. 265: 141–70. doi:10.1016/j.jcz.2016.06.002.
  4. ^ a b c 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): 239–71. doi:10.1016/j.jcz.2004.09.001.
  5. ^ a b c Ruppert, Edward E.; Fox, Richard S.; Barnes, Robert D., eds. (2004). Invertebrate Zoology (7th ed.). p. 776. ISBN 978-0-03-025982-1.
  6. ^ Heiner, Iben. "Preliminary account of the Loriciferan fauna of the Faroe Bank (NE Atlantic)". Annales Societatis Scientiatum Færoensis Supplementum. 41: 213–9.
  7. ^ a b Heiner, Iben; Kristensen, Reinhardt Møbjerg (18 March 2005). "Two new species of the genus Pliciloricus (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic". Zoologischer Anzeiger. 243 (3): 121–38. doi:10.1016/j.jcz.2004.05.002.
  8. ^ a b c d Kristensen, R. M. (July 2002). "An Introduction to Loricifera, Cycliophora, and Micrognathozoa". Integrative and Comparative Biology. 42 (3): 641–51. doi:10.1093/icb/42.3.641. PMID 21708760.
  9. ^ Heiner, Iben; Sorensen, Martin Vinther; Kristensen, Reinhardt Mobjerg (2004). Loricifera (Girdle Wearers) in Grzimek's Animal Life Encyclopedia Volume 1. New York, NY: Van Nostrand Reinhold Company. p. 343–350.
  10. ^ "Discovery of new fossil from half billion years ago sheds light on life on Earth: Scientists find 'unfossilizable' creature".
  11. ^ 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.
  12. ^ 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): 332–40. doi:10.1666/09-102R.1. JSTOR 40605520.
  13. ^ 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. doi:10.1038/s41559-016-0022. hdl:2381/38658.
  14. ^ Fang, Janet (8 April 2010). "Animals thrive without oxygen at sea bottom". Nature. 464 (7290): 825. doi:10.1038/464825b. PMID 20376121.
  15. ^ Milius, Susan (9 April 2010). "Briny deep basin may be home to animals thriving without oxygen". Science News.
  16. ^ 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.

Further reading

Australoricus

Australoricus oculatus is a species of Loricifera, a species of microscopic marine sediment-dwelling animals, in the family Nanaloricidae. It is the only described species in the genus Australoricus. It was discovered in sea caves off New South Wales in Australia.

Ecdysozoa

Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes. A large study in 2008 by Dunn et al. strongly supported the Ecdysozoa as a clade, that is, a group consisting of a common ancestor and all its descendants.The group is also supported by morphological characters, and includes all animals that grow by ecdysis, moulting their exoskeleton.

The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques, while others contested the interpretation of the molecular data.

Micro-animal

Micro-animals are animals so small that they can be visually observed only under a microscope. Microscopic arthropods include dust mites, spider mites, and some crustaceans such as copepods and certain cladocera. Another common group of microscopic animals are the rotifers, which are filter feeders that are usually found in fresh water. Some nematode species are microscopic, as well as many loricifera, including the recently discovered anaerobic species, which spend their entire lives in an anoxic environment.

Nanaloricus

Nanaloricus is a genus of Loriciferan, the first to be described.

Phoeniciloricus

Phoeniciloricus is a monospecific genus of loriciferans, a phylum of small marine sediment-dwelling animals. Its one species is Phoeniciloricus simplidigitatus.

Pliciloricidae

Pliciloricidae are a family of marine organisms in the phylum Loricifera. It contains 22 species in 3 genera.

Pliciloricus

Pliciloricus is a genus of marine organisms Pliciloricidae family, the phylum Loricifera described by Higgins & Kristensen, 1986.

Pliciloricus dubius

Pliciloricus dubius is a marine Loriciferan species of genus Pliciloricus described by Higgins & Kristensen 1986.

Pliciloricus enigmaticus

Pliciloricus enigmaticus is a marine Loriciferan species of genus Pliciloricus described by Higgins & Kristensen 1986.

Reinhardt Kristensen

Reinhardt Møbjerg Kristensen (born 1948) is a Danish invertebrate biologist, noted for the discovery of three new phyla of microscopic animals: the Loricifera in 1983, the Cycliophora in 1995, and the Micrognathozoa in 2000. He is also considered one of the world's leading experts on tardigrades. His recent field of work revolves mostly around arctic biology.

He is also known for documenting Dendrogramma, an invertebrate genus that was later classified as Siphonophorae of the family Rhodaliidae.

Rugiloricus

Rugiloricus is a genus of marine organisms of the phylum Loricifera and the family Pliciloricidae, described by Higgins & Kristensen in 1986.

Rugiloricus cauliculus

Rugiloricus cauliculus is a species of marine animal of the phylum Loricifera and the family Pliciloricidae. The species was described by Higgins & Kristensen in 1986, however other sources such as OBIS indicate that discovery of the species occurred on 19th November 1983.

Scalidophora

Scalidophora is a group of marine pseudocoelomate protostomes that was proposed on morphological grounds to unite three phyla: the Kinorhyncha, the Priapulida and the Loricifera. The three phyla have four characters in common — chitinous cuticle that is moulted, rings of scalids on the introvert, flosculi, and two rings of introvert retracts. However, the monophyly of the Scalidophora is not supported by molecular studies, where the position of the Loricifera was uncertain or as sister to the Panarthropoda. Both studies supported a reduced Scalidophora comprising the Kinorhyncha and Priapulida as sister phyla. Their closest relatives are the Panarthropoda, Nematoda and Nematomorpha; thus they are placed in the group Ecdysozoa.

The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem Scalidophorans.

The group has also been considered a single group, Cephalorhyncha, with three classes.

The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).

Spinoloricus

Spinoloricus is a genus of nanaloricid loriciferans. Its type species is S. turbatio, described in 2007, and another species, native to completely anoxic environment, Spinoloricus cinziae, was described in 2014.

Spinoloricus cinziae

Spinoloricus cinziae is an animal species described in 2014 in the phylum Loricifera.It is the first animal species described that does not require oxygen at any point during its life. The species, along with two other newly discovered species, Rugiloricus nov. sp. and Pliciloricus nov. sp., were found in the sediment of the anoxic L'Atalante basin of the Mediterranean Sea.Electron microscope images show that the species' cellular innards appear to be adapted for a zero-oxygen life. Their mitochondria appear to act as hydrogenosomes, organelles which provide energy in some anaerobic single-celled creatures.With a visual resemblance to tiny cups with tentacles sticking out, the species has been said to look like something out of a Dr. Seuss book.At adulthood, this species is characterized by a mouth cone with eight oral ridges, a neck with eight single trichoscalids alternating with seven double trichoscalids, as well as lorical plates with spikes located at the corners.

More than 30 species in this group have been described.

Symbion

Symbion is the name of a genus of aquatic animals, less than 0.5 mm wide, found living attached to the bodies of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-stage life-cycle. They appear so different from other animals that they were assigned their own, new phylum Cycliophora shortly after they were discovered in 1995. This was the first new phylum of multicelled organism to be discovered since the Loricifera in 1983.

Tenuiloricus

Tenuiloricus is a genus of loriciferans known from its larval form, and occupying an uncertain taxonomic position.

Titaniloricus

Titaniloricus is a genus of small marine animal in the phylum Loricifera. It contains a single species, Titaniloricus inexpectatovus, described by Gunnar Gad in 2005. It has been collected from the abyssal plain in Angolan waters of the Atlantic Ocean.

Vinctiplicata

The Vinctiplicata is a clade of Scalidophora uniting the Loricifera and the Priapulida, and representing the sister group to the Kinorhyncha. Its monophyly is supported on morphological grounds, although recent molecular studies indicate that the Loricifera may be more closely related to the Nematomorpha.

Extant Animal phyla
Extant life phyla/divisions by domain

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