Loricifera
Encyclopedia
Loricifera is a phylum
of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca. 1 mm. 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
. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.
s of pliciloricids include also paedogenetic stages with different forms of parthenogenetic
reproduction. They are not known to be present in the fossil record.
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. However, mounting molecular evidence indicates a closer relationship with the nematomorpha
.
. 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.
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 they rely on hydrogenosome
s (or similar organelles) instead of on mitochondria for energy.
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. 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. As a consequence, this environment is completely anoxic and, due to the activity of sulphate reducers, contains sulphide at a concentration of 2.9 mM. 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 heterotroph
s at the next trophic level
.
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca. 1 mm. They are characterised by a protective outer case called a lorica
Lorica (biology)
In biology, a lorica is a shell-like protective outer covering, often reinforced with sand grains and other particles that some protozoans and loricifera metazoans secrete. Usually it is tubular or conical in shape, with a loose case that is closed at one end. An example is the protozoan genus...
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
Reinhardt Kristensen
Reinhardt Møbjerg Kristensen 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...
, in Roscoff
Roscoff
Roscoff is a commune in the Finistère department of Brittany in northwestern France.The nearby Île de Batz, called Enez Vaz in Breton, is a small island that can be reached by launch from the harbour....
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.
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. There is no circulatory system and no endocrine system. Many of the larvae are acoelomate, with some adults being pseudocoelomate, and some remaining acoelomate. 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 cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
s of pliciloricids include also paedogenetic stages with different forms of parthenogenetic
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
reproduction. They are not known to be present in the fossil record.
Taxonomic affinity
Morphological studies have traditionlally placed the phylum in the vinctiplicataVinctiplicata
The Vinctiplicata is a clade of scalidophoran 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...
with the Priapulida
Priapulida
Priapulida is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis...
; this plus the Kinorhyncha
Kinorhyncha
Kinorhyncha is a phylum of small marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos...
constitutes the taxon Scalidophora
Scalidophora
Scalidophora is a group of marine pseudocoelomate invertebrates, consisting of the three phyla Kinorhyncha, Priapulida, and Loricifera. The members of the group share a number of characteristics, including introvert larvae and moulting of the cuticle...
. The three phyla share four characters in common — chitinous cuticle, rings of scalids on the introvert, flosculi, and two rings of introvert retracts. However, mounting molecular evidence indicates a closer relationship with the nematomorpha
Nematomorpha
Nematomorpha is a phylum of parasitic animals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from long and can reach in extreme cases up to 2 metres, and in diameter...
.
Evolutionary history
The loricates are believed to be miniaturized descendants of a larger organism perhaps resembling the Cambrian fossil SiriloricaSirilorica
Sirilorica is a monospecific genus of stem-group scalidophoran from the Sirius Passet.- Morphology :Sirilorica was a worm-like animal ranging from three to eight centimetres in length.- Ecology :...
. 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.
In anoxic environment
Three species of Loricifera have been found in the sediments at the bottom of the L'Atalante basinL'Atalante basin
L'Atalante basin is a hypersaline brine lake at the bottom of the Mediterranean Sea about west of the island of Crete. It is named for one of the oceanographic research vessels involved in its discovery in 1993...
in Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, 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 they rely on hydrogenosome
Hydrogenosome
A hydrogenosome is a membrane-enclosed organelle of some anaerobic ciliates, trichomonads and fungi. The hydrogenosomes of trichomonads produce molecular hydrogen, acetate, carbon dioxide and ATP by the combined actions of pyruvate:ferredoxin oxido-reductase, hydrogenase, acetate:succinate CoA...
s (or similar organelles) instead of on mitochondria for energy.
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. 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. As a consequence, this environment is completely anoxic and, due to the activity of sulphate reducers, contains sulphide at a concentration of 2.9 mM. 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 heterotroph
Heterotroph
A heterotroph is an organism that cannot fix carbon and uses organic carbon for growth. This contrasts with autotrophs, such as plants and algae, which can use energy from sunlight or inorganic compounds to produce organic compounds such as carbohydrates, fats, and proteins from inorganic carbon...
s at the next trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
.
Armorloricus
- Armorloricus davidi Kristensen & Gad, 2004
- Armorloricus elegans Kristensen & Gad, 2004
- Armorloricus kristenseni Heiner, 2004
Nanaloricus
- Nanaloricus khaitatus Todaro & Kristensen, 1998
- Nanaloricus mysticus Kristensen, 1983
Pliciloricus
- Pliciloricus cavernicola
- Pliciloricus corvus Gad, 2005
- Pliciloricus dubius Higgins & Kristensen, 1986
- Pliciloricus enigmaticus Higgins & Kristensen, 1986
- Pliciloricus gracilis Higgins & Kristensen, 1986
- Pliciloricus hadalis Kristensen & Shirayama 1988
- Pliciloricus leocaudatus Heiner & Kristensen, 2005
- Pliciloricus orphanus Higgins & Kristensen, 1986
- Pliciloricus pedicularis Gad 2005
- Pliciloricus profundus Higgins & Kristensen, 1986
- Pliciloricus senicirrus Gad, 2005
- Pliciloricus shukeri Heiner & Kristensen, 2005
Rugiloricus
- Rugiloricus carolinensis Higgins & Kristensen, 1986
- Rugiloricus cauliculus Higgins & Kristensen, 1986
- Rugiloricus ornatus Higgins & Kristensen, 1986
- Rugiloricus polaris Gad and Arbizu, 2005