''Didinium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s with at least ten accepted species. All are free-living

carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

. Most are found in fresh and

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

water, but three marine

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

are known. Their diet consists largely of ''

Paramecium '' ''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and marine environments and a ...

'', although they will also attack and consume other ciliates. Some species, such as ''D. gargantua'', also feed on non-ciliate

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...

s, including

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

cryptomonad The cryptomonads (or cryptophytes) are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterio ...

s, and

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

Appearance and reproduction

''Didinia'' are rounded, oval or barrel-shaped and range in length from 50 to 150

micrometres The micrometre (American and British English spelling differences#-re, -er, international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American and British English spelling differences# ...

. The cell body is encircled by two ciliary bands, or ''pectinelles'', an upper band and a lower band just below the midline. This distinguishes them from the related genus '' Monodinium'', which have only a single band, except during

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

. The pectinelles are used to move ''Didinium'' through water by

rotating Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...

the cell around its axis. At the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end, a cone-shaped structure protrudes, supported by a palisade of stiff microtubular rods (nematodesmata). This cone encloses the

cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuole ...

or "mouth" opening, as in other haptorian ciliates. The dimensions of this protuberance vary among the different species. The

macronucleus A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, such as metabolism. During conjugation, t ...

is long, and may be curved, horseshoe-shaped or twisted into a shape resembling a figure eight. A

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contractile va ...

and anal aperture are in the posterior of the cell. Like all ciliates, ''Didinia''

reproduce Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...

asexually via

binary fission Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that t ...

, or

sex Sex is the trait that determines whether a sexually reproducing animal or plant produces male or female gametes. Male plants and animals produce smaller mobile gametes (spermatozoa, sperm, pollen), while females produce larger ones (ova, oft ...

ually through

conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...

''Didinium nasutum''

Much of what has been published about this genus is based on numerous studies of a single species, ''Didinium nasutum''. A voracious predator, ''D. nasutum'' uses specialized structures called toxicysts to ensnare and paralyze its ciliate prey. Once captured, the prey is engulfed through ''Didiniums expandible

. While ''D. nasutum'' is sometimes described as feeding exclusively upon ''

'', it has been shown that the organism will readily devour other ciliate species, including ''

Colpoda Colpoda is a genus of ciliates in the class Colpodea, order Colpodida, and family Colpodidae. Description ''Colpoda'' are distinctly reniform (kidney-shaped) and are strongly convex on one side, concave on the other. The concave side often ...

'', ''Colpidium campylum'', ''

Tetrahymena pyriformis ''Tetrahymena pyriformis'' is a species of Ciliophora in the family Tetrahymenidae Tetrahymenidae is a family of ciliates. References Ciliate families Oligohymenophorea {{ciliate-stub .... It is one of the most commonly ciliated mod ...

'', '' Coleps hirtus'' and ''

Lacrymaria olor ''Lacrymaria olor'' is a species of ciliates, typically long, that is found in freshwater ponds. Its name means "swan tear" in Latin, and refers to its general shape: namely, a teardrop-shaped cell with a small "head" at the end of a long slende ...

''. Moreover, strains of ''Didinium'' raised on a ''Colpidium campylum'' will actually show a preference for a diet made up of that species, as well as a diminished ability to kill and ingest ''Paramecia''. In the absence of food, ''D. nasutum'' will

encyst A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist or rarely an invertebrate animal, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of ...

, lying dormant within a protective coating. In the laboratory, other environmental stimuli, such as the age of the growth medium or the accumulation of certain metabolic waste products, can also trigger encystment. When the encysted form of ''D. nasutum'' is exposed to a vigorous culture of ''Paramecium'', it will excyst, reverting to its active, swimming form. Didinium cysts have been shown to remain viable for at least 10 years.

History and classification

''Didinium'' was discovered by the eighteenth-century naturalist O.F. Müller and described in his ''Animalcula Infusoria'' under the name ''Vorticella nasuta''. In 1859,

Samuel Friedrich Stein Samuel Friedrich Nathaniel Ritter von Stein (November 3, 1818 – January 9, 1885) was a German entomologist. He was Professor at the Royal Saxon Academy of Forestry in Tharandt from 1850–55; and Professor, and later Rector, at the Charles Unive ...

moved the species to the newly created genus ''Didinium'', which he placed within the order

Peritrich The peritrichs (Latin: Peritrichia) are a large and distinctive group of ciliates. The peritrichs were first defined by Friedrich von Stein in 1859. Initially they were considered spirotrichs, then treated as a separate category, before receiving ...

a, alongside other ciliates which have a ciliary fringe at the anterior of the cell such as

Vorticella ''Vorticella'' is a genus of bell-shaped ciliates that have stalks to attach themselves to substrates. The stalks have contractile myonemes, allowing them to pull the cell body against substrates. The formation of the stalk happens after the fr ...

and Cothurnia. Later in the century, under the

taxonomical In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...

scheme created 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. ...

, ''Didinium'' was removed from among the Peritrichs, and placed in the order '' Holotricha''. In 1974, John. O. Corliss created the order Haptorida, within the subclass Haptoria, for "rapacious carnivorous forms" such as ''Didinium'', ''

Dileptus ''Dileptus'' is a genus of unicellular ciliates in the class Litostomatea. Species of ''Dileptus'' occur in fresh and salt water, as well as mosses and soils. Most are aggressive predators equipped with long, mobile proboscides lined with toxic ...

'' and '' Spathidium''. This group has since been placed in the class

Litostomatea The Litostomatea are a class of ciliates. The group consists of three subclasses: Haptoria, Trichostomatia and Rhynchostomatia. Haptoria includes mostly carnivorous forms such as ''Didinium'', a species of which preys primarily on the ciliate ''P ...

Small & Lynn, 1981.

Genetic analysis Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research, and these are also considered parts of ...

of Haptorian ciliates has shown that they do not form 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 ...

group.

List of Species

'' Didinium alveolatum'' Kahl, 1930
'' Didinium armatum'' Penard, 1922
'' Didinium balbianii Fabre-Domergue, 1888 ''
'' Didinium bosphoricum Hovasse, 1932
'' Didinium chlorelligerum'' Kahl, 1935
'' Didinium faurei'' Kahl, 1930
''

Didinium gargantua ''Didinium'' is a genus of unicellular ciliates with at least ten accepted species. All are free-living carnivores. Most are found in fresh and brackish water, but three marine species are known. Their diet consists largely of ''Paramecium'', ...

'' Meunier, 1910
'' Didinium impressum'' Kahl, 1926
'' Didinium minimum''
'' Didinium nasutum'' (Müller, 1773) Stein, 1859

References

* {{Taxonbar, from=Q93422 Ciliate genera Litostomatea