| Loxodes | |
|---|---|
.jpg) | |
| Illustration ofLoxodes rostrum | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Alveolata |
| Phylum: | Ciliophora |
| Subphylum: | Postciliodesmatophora |
| Class: | Karyorelictea |
| Order: | Loxodida |
| Family: | Loxodidae |
| Genus: | Loxodes Ehrenberg, 1830 |
| Species | |
Several, including:[1] | |
Loxodes is a genus ofkaryorelicteanciliates, belonging toLoxodidae.[1] It is the only known karyorelictean ciliate that lives in freshwater habitats.
The termLoxodes derives from theancient greekλοξός (loxós), meaning "oblique, tilted".[2][3]
Loxodes lives infreshwater habitats such as lakes and ponds, unlike other karyorelictean ciliates such as the other loxodid genusRemanella, which live in brackish-water or marine habitats.[4] They feed on bacteria and protists such asmicroalgae.[5] It ismicroaerobic, 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 usenitrate instead of oxygen as an electron acceptor forrespiration.[6]Nitrate respiration is rare among eukaryotes, andLoxodes was the first eukaryote known to have this capability.Loxodes is also sensitive to light.
Both genera in the family Loxodidae have organelles known asMüller (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. InLoxodes, the statolith is mostly composed ofbarium salts, compared toRemanella, where they are mostly strontium. Its structure and function resembles thestatocyst of some animals.[4]Loxodes uses its Müller's vesicle to distinguish between up and down (geotaxis orgravitaxis), 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.[7]
![Species of Loxodes containing significantly large green-colored algae. Scale bar: 10 μm.[8]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aLoxodes.png)
![Detail showing a Müller vesicle (top arrow).[8]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aM%25C3%25BCller_vesicle.png)
Loxodes uses a variant of the standardgenetic code, where the stop codons UAA and UAG have been reassigned to the amino acidglutamine. Thisvariant code is also used by other ciliates.[9]
Unlike other ciliates, the macronuclei ofkaryorelicteans do not divide. This was first observed inLoxodes byOtto Bütschli in the 1870s.[10] It was later shown to be a distinctive feature of the class Karyorelictea in general. Experiments onLoxodes have shown that little or noDNA synthesis occurs in their macronuclei, and that the DNA content of a macronucleus is only slightly more than that of adiploid micronucleus ("paradiploid").[10]
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Data related toLoxodes at Wikispecies