''Loxodes'' is a genus of

karyorelictea Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, '' Loxodes'', is fou ...

n ciliates, belonging to family

Loxodidae Loxodidae is a family of karyorelict ciliates. Loxodidae members possess an elongated, laterally flattened shape. They share two key characters: a beak-like anterior rostrum interrupting the perioral kineties, and peculiar cytoplasmic organelles ...

. It is the only known karyorelictean ciliate that lives in freshwater habitats. The term ''Loxodes'' derives from the

ancient greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...

(), meaning "oblique, tilted".

Ecology

''Loxodes'' lives in

freshwater habitat Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be ...

s such as lakes and ponds, unlike other karyorelictean ciliates such as the other loxodid genus '' Remanella'', which live in brackish-water or marine habitats. They feed on bacteria and protists such as

microalgae Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist indi ...

. It is microaerobic, preferring low concentrations of oxygen, below 5% atmospheric saturation. It can also survive extended periods in anoxic water, where oxygen is absent. Under such conditions, ''Loxodes'' is able to use

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble ...

instead of oxygen as an electron acceptor for respiration. Nitrate respiration is rare among eukaryotes, and ''Loxodes'' was the first eukaryote known to have this capability. ''Loxodes'' is also sensitive to light.

Geotaxis

Both genera in the family Loxodidae have organelles known as

Müller Müller may refer to: * ''Die schöne Müllerin'' (1823) (sometimes referred to as ''Müllerlieder''; ''Müllerin'' is a female miller) is a song cycle with words by Wilhelm Müller and music by Franz Schubert * Doctor Müller, fictional character ...

(or Müllerian) vesicles, which are involved in the sensing of gravity. They are about 7 µm across, and contain a membrane-covered mineral body known as a statolith. In ''Loxodes'', the statolith is mostly composed of

barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. ...

salts, compared to ''Remanella'', where they are mostly strontium. Its structure and function resembles the

statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, and crustaceans. A similar structure is also found in ''Xenoturbella''. The statocyst cons ...

of some animals. ''Loxodes'' uses its Müller's vesicle to distinguish between up and down (

geotaxis Gravitaxis (or ''geotaxis'') is a form of taxis characterized by the directional movement of an organism in response to gravity. Gravitaxis is one of the many forms of taxis. It is characterized by the movement of an organism in response to gravit ...

gravitaxis Gravitaxis (or ''geotaxis'') is a form of taxis characterized by the directional movement of an organism in response to gravity. Gravitaxis is one of the many forms of taxis. It is characterized by the movement of an organism in response to gravita ...

), which it uses as a stimulus in addition to the oxygen concentration to orient itself in the water column. When oxygen concentrations are high, ''Loxodes'' tends to swim downwards, and vice versa. File:Loxodes.png, Species of ''Loxodes'' containing significantly large green-colored algae. Scale bar: 10 µm. File:Müller vesicle.png, Detail showing a Müller vesicle (top arrow). File:Инфузория Loxodes съедает длинную цианобактерию.webm, ''Loxodes'' ciliate eating a long cyanobacteria

Genetic code

''Loxodes'' uses a variant of the standard

genetic code The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...

, where the stop codons UAA and UAG have been reassigned to the amino acid

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

. This variant code is also used by other ciliates.

Cell cycle

Unlike other ciliates, the macronuclei of

ns do not divide. This was first observed in ''Loxodes'' by

Otto Bütschli Johann Adam Otto Bütschli (3 May 1848 – 2 February 1920) was a German zoologist and professor at the University of Heidelberg. He specialized in invertebrates and insect development. Many of the groups of protists were first recognized by him. ...

in the 1870s. It was later shown to be a distinctive feature of the class Karyorelictea in general. Experiments on ''Loxodes'' have shown that little or no

DNA synthesis DNA synthesis is the natural or artificial creation of deoxyribonucleic acid (DNA) molecules. DNA is a macromolecule made up of nucleotide units, which are linked by covalent bonds and hydrogen bonds, in a repeating structure. DNA synthesis occur ...

occurs in their macronuclei, and that the DNA content of a macronucleus is only slightly more than that of a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respecti ...

micronucleus ("paradiploid").

References

External links

* {{Taxonbar, from=Q1981570 Karyorelictea Ciliate genera