''Didinium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

. 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 A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

are known. Their diet consists largely of ''

Paramecium ''Paramecium'' ( , , plural "paramecia" only when used as a Common name, vernacular name) is a genus of eukaryotic, unicellular ciliates, widespread in freshwater, brackish, and Ocean, marine environments. Paramecia are often abundant in stagna ...

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

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s, including

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

cryptomonad The cryptomonads (or cryptophytes) are a superclass of algae, most of which have plastids. They are traditionally considered a division of algae among phycologists, under the name of Cryptophyta. They are common in freshwater, and also occur ...

s, and

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

Appearance and reproduction

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

micrometres The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

. 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 rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersec ...

the cell around its axis. At the

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

end, a cone-shaped structure protrudes, supported by a palisade of stiff

microtubular Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

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 vacu ...

, 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 Metabolism (, ...

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, including unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contrac ...

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

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

sex Sex is the biological trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inheri ...

ually after undergoing

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 change o ...

''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 by ''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, and concave on the other. The concave side ...

'', ''Colpidium campylum'', '' Tetrahymena pyriformis'', '' Coleps hirtus'', and '' Lacrymaria olor''. 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, that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. ...

, 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

In the 18th century, ''Didinium'' was discovered by the 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 Uni ...

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

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 Haptorian ciliates has shown that they do not form a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

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

References

* {{Authority control Ciliate genera Litostomatea