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 named Müller vesicles. The extensive development of lacunae of the

smooth endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

leads to strong vacuolization of the endoplasm. This feature is associated to a lack of contractile vacuoles in all loxodids. The term ''Loxodidae'' 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 peri ...

(), meaning "oblique, tilted".

Gravitaxis

Loxodidae members possess the ability to orient themselves in oxygen gradients. They use

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

as a

stimulus A stimulus is something that causes a physiological response. It may refer to: *Stimulation **Stimulus (physiology), something external that influences an activity **Stimulus (psychology), a concept in behaviorism and perception *Stimulus (economi ...

for this spatial orientation, a phenomenon called

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 ...

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 gravita ...

. Loxodid ciliates must therefore have developed

mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, a ...

informing them about what is up or down. A likely candidate structure for their gravitaxis is the Müller vesicle.

Müller vesicle

Müller vesicles (also known as Müllerian vesicles, or spelled ''Mueller'') are statocyst-like organelles uniquely found in ciliates of the family Loxodidae. They are named after the Danish zoologist

Otto Friedrich Müller Otto Friedrich Müller, also known as Otto Friedrich Mueller (2 November 1730 – 26 December 1784) was a Danish naturalist and scientific illustrator. Biography Müller was born in Copenhagen. He was educated for the church, became tutor to a yo ...

Eugène Penard Eugène Penard (16 September 1855 – 5 January 1954) was a Swiss biologist and pioneer in systematics of the amoebae. Penard was born in Geneva where his father ran a private school. After studying in Geneva, Eugène worked in a bank but decided ...

was the first to propose that these vesicles were analogous to

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 ...

s, which are the gravity-sensing structures of animals. Each Müller vesicle is spherical, about 7 µm across (in ''Loxodes''), and is bounded by a membrane. It contains a Müller body, which comprises mineral concretions in an organic matrix bounded by a membrane, that is suspended in a vacuole by a stalk. The stalk is about 0.3–0.4 µm thick, and contains microtubules that connect the Müller body with the adjacent kinety, which is believed to help transmit the sensory signal to the rest of the cell. The mineral concretions are mostly salts of

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...

in the genus ''

Remanella ''Remanella'' is a genus of karyorelict ciliates, belonging to family Loxodidae. Whereas ''Remanella'' inhabits brackish and marine waters, '' Loxodes'' – the other loxodid genus – is a freshwater taxon. Etymology The genus name is a pa ...

'', but

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. Th ...

in ''

Loxodes ''Loxodes'' is a genus of karyorelictean ciliates, belonging to family Loxodidae. It is the only known karyorelictean ciliate that lives in freshwater habitats. The term ''Loxodes'' derives from the ancient greek (), meaning "oblique, tilted". ...

''.

Phylogeny

Molecular phylogeny based on sequences of the SSU rRNA gene indicates that ''Remanella'' and ''Loxodes'' branch together into a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

family Loxodidae.

References

External links

* {{Taxonbar, from=Q18573101 Karyorelictea Ciliate families