Limnognathia
Encyclopedia
Limnognathia maerski is a microscopic animal, discovered living in homothermic spring
s on Disko Island
, Greenland
in 1994, that has variously been assigned as a class
or subphylum
in the phylum
Gnathifera
or as a phylum in a Gnathifera superphylum, named Micrognathozoa. It is related to the rotifer
s and gnathostomulid
s, grouped together as the Gnathifera. With an average length of one-tenth of a millimetre, it is one of the smallest animals known.
L. maerski has very complicated jaws, with fifteen separate elements. The parts of the jaw structure are connected by ligaments and muscles. The jaw parts are very small, ranging from 4 μm
to 14 μm. The animal can extend part of its jaw structure outside of its mouth while eating. It also extends much of its jaw structure outside of its mouth when it is regurgitating items that are indigestible.
L. maerski has a large ganglion
, or 'brain', in its head, and paired nerve cords extending ventrally (along the lower side of the body) towards the tail. Stiff sensory bristles made up of one to three cilia
are scattered about the body. These bristles are similar to ones found on gnathostomulids, but up to three cilia may arise from a single cell in L. maerski, while gnathostomulids never have more than one cilium per cell.
Flexible cilia are arranged in a horseshoe-shaped area on the forehead, and in spots on the sides of the head and in two rows on the underside of the body. The cilia on the forehead create a current that moves food particles towards the mouth. The other cilia move the animal.
All specimens of L. maerski that have been collected have had female organs. They lay two kinds of eggs: thin-walled eggs that hatch quickly, and thick-walled eggs that are believed to be resistant to freezing, and thus capable of over-wintering and hatching in the spring. The same pattern is known from rotifers, where thick-walled eggs only form after fertilization by males. The youngest L. maerski specimens collected may also have male organs, and it is now theorized that the animals hatch as males and then become females.
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...
s on Disko Island
Disko Island
Disko Island is a large island in Baffin Bay, off the west coast of Greenland. It has an area of , making it the second largest island of Greenland and one of the 100 largest islands in the world...
, Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
in 1994, that has variously been assigned as a class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
or subphylum
Subphylum
In life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum.Not all phyla are divided into subphyla...
in the phylum
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....
Gnathifera
Gnathifera (phylum)
Gnathifera is an assemblage of phyla of metazoans."Acanthognatha" is a similar grouping, including rotifers, acanthocephalans, gastrotrichs, and gnathostomulids....
or as a phylum in a Gnathifera superphylum, named Micrognathozoa. It is related to the rotifer
Rotifer
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...
s and gnathostomulid
Gnathostomulid
Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956....
s, grouped together as the Gnathifera. With an average length of one-tenth of a millimetre, it is one of the smallest animals known.
L. maerski has very complicated jaws, with fifteen separate elements. The parts of the jaw structure are connected by ligaments and muscles. The jaw parts are very small, ranging from 4 μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
to 14 μm. The animal can extend part of its jaw structure outside of its mouth while eating. It also extends much of its jaw structure outside of its mouth when it is regurgitating items that are indigestible.
L. maerski has a large ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
, or 'brain', in its head, and paired nerve cords extending ventrally (along the lower side of the body) towards the tail. Stiff sensory bristles made up of one to three cilia
Cilium
A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....
are scattered about the body. These bristles are similar to ones found on gnathostomulids, but up to three cilia may arise from a single cell in L. maerski, while gnathostomulids never have more than one cilium per cell.
Flexible cilia are arranged in a horseshoe-shaped area on the forehead, and in spots on the sides of the head and in two rows on the underside of the body. The cilia on the forehead create a current that moves food particles towards the mouth. The other cilia move the animal.
All specimens of L. maerski that have been collected have had female organs. They lay two kinds of eggs: thin-walled eggs that hatch quickly, and thick-walled eggs that are believed to be resistant to freezing, and thus capable of over-wintering and hatching in the spring. The same pattern is known from rotifers, where thick-walled eggs only form after fertilization by males. The youngest L. maerski specimens collected may also have male organs, and it is now theorized that the animals hatch as males and then become females.