Limnognathia is a genus of microscopic acoelomate freshwater animal that was discovered in Disko Island, Greenland, in 1994.[ Gastrotricha and Gnathifera] Since then, it has also been found on the Crozet Islands of Antarctica as well as in the British Isles and the Spanish Pyrenees,[Worsaae and Kristensen, 2016] There are two known species of Limnognathia: L. maerski, described in 2000, and L. desmeti, described in 2025.
Limnognathia is the Monotypic taxon in the phylum Micrognathozoa ("small-jawed animal").
Description
Feeding
Limnognathia mainly feeds on bacteria, blue-green algae, and
Diatom. It has complex jaws, with fifteen separate elements; these elements are very small, ranging from 4
Micrometre to 14 μm. The animal can extend part of its jaw outside its mouth while eating. It also extends much of its jaw outside its mouth when it is regurgitating indigestible items.
Anatomy
Limnognathia has a large
ganglion, or 'brain', in its head, and paired nerve cords extending along the lower side of the body towards the tail. Stiff sensory bristles made up of one to three
cilium 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
Limnognathia, while gnathostomulids have only 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, while the other cilia move the animal.
Reproduction
All specimens of
Limnognathia 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
overwintering and hatching in the spring. The same pattern is known from
rotifers, where thick-walled eggs only form after fertilization by males. The youngest
Limnognathia specimens collected may also have
male organs, and it is now hypothesized that the animals hatch as males and later become females, a process called sequential hermaphroditism.
Taxonomy and phylogeny
Taxonomic status
Limnognathia is nominally a
, but has variously been assigned as a class or
subphylum in the clade Gnathifera or as a phylum in a Gnathifera
superphylum, named
Micrognathozoa. It is related to the
and
gnathostomulids, grouped together as the Gnathifera.
Two species are described:
Limnognathia maerski from Greenland and Spain, and
Limnognathia desmeti from the Crozet Islands. The two species have no recognizable morphological differences, but genetic studies have shown them to be distinct.
Species
-
Limnognathia maerski (Kristensen & Funch, 2000)
-
Limnognathia desmeti (Worsaae & Møller, 2025)
Phylogeny
Cladogram
showing the relationships of
Limnognathia:
The Gnathifera is the sister group to the Platytrochozoa and is crucial to understand because of its relationship to animal evolution.
External links
-
— Comprehensive information on L. maerski
