Didinium nasutum CGI illustration by Denis Zarubin, 2021
Didinia are rounded, oval, or barrel-shaped and range in length from 50 to 150 micrometres.[3] The cell body is encircled by two ciliary bands, or pectinelles, an upper band and a lower band just below the midline.[4] This distinguishes them from the related genus Monodinium, which have only a single band, except during cell division.[5] The pectinelles are used to move Didinium through water by rotating the cell around its axis.[6] At the anterior end, a cone-shaped structure protrudes, supported by a palisade of stiff microtubular rods (nematodesmata). This cone encloses the cytostome, or "mouth" opening, as in other haptorian ciliates. The dimensions of this protuberance vary among the different species.
Didinium nasutum consuming a Paramecium. Illustration by S. O. Mast, 1909
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 Didinium's expandible cytostome.[9]
While D. nasutum is sometimes described as feeding exclusively upon Paramecium, it has been shown that the organism will readily devour other ciliate species, including Colpoda, Colpidium campylum, Tetrahymena pyriformis, Coleps hirtus, and Lacrymaria olor.[1][10] 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.[1]
In the absence of food, D. nasutum will encyst, lying dormant within a protective coating.[11] 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.[12] When the encysted form of D. nasutum is exposed to a vigorous culture of Paramecium, it will excyst, reverting to its active, swimming form.[13]
Didinium cysts have been shown to remain viable for at least 10 years.[14]
In the 18th century, Didinium was discovered by the naturalist O.F. Müller and described in his Animalcula Infusoria under the name Vorticella nasuta.[15] In 1859, Samuel Friedrich Stein 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 and Cothurnia.[16] Later in the century, under the taxonomical scheme created by Otto Bütschli, Didinium was removed from among the Peritrichs, and placed in the order Holotricha.[17] In 1974, John O. Corliss created the order Haptorida, within the subclass Haptoria, for "rapacious carnivorous forms" such as Didinium, Dileptus, and Spathidium.[18] This group has since been placed in the class Litostomatea Small & Lynn, 1981.
^ abcBerger, Jacques (October 1979). "The Feeding Behavior of Didinium nasutum on an Atypical Prey Ciliate (Colpidium campylum)". Transactions of the American Microscopical Society. 98 (4): 487–94. doi:10.2307/3225898. JSTOR3225898.
^Kahl, Alfred (1930–35). F. Dahl (ed.). Urtiere oder Protozoa I: Wimpertiere oder Ciliata (Infusoria) In: Die Tierwelt Deutschlands. Vol. 1. Allgemeiner teil und Prostomata. Jena: G. Fischer. pp. 123–6.
^Lee, John J.; et al. (2000). John J. Lee; Gordon F. Leedale; Phyllis Bradbury (eds.). An Illustrated Guide to the Protozoa: organisms traditionally referred to as protozoa, or newly discovered groups. Vol. 1 (2 ed.). Lawrence, Kansas: Society of Protozoologists. pp. 480–1. ISBN1-891276-22-0.
^Beers, C. Dale (March 1927). "Factors involved in encystment in the ciliate didinium nasutum". Journal of Morphology. 43 (2): 499–520. doi:10.1002/jmor.1050430208. S2CID83902868.
^Beers, C. Dale (Sep–Oct 1937). "The Viability of Ten-Year-Old Didinium Cysts (Infusoria)". The American Naturalist. 71 (736): 521–4. doi:10.1086/280739. JSTOR2457306. S2CID83784747.
^Bütschli, Otto (1887–1889). Bronn, H. G. (ed.). ERSTER BAND. PROTOZOA. Vol. III. Leipzig & Heidelberg: C. F. Winter. p. 1688. {{cite book}}: |work= ignored (help)
^Corliss, John O. (May 1974). "Remarks on the Composition of the Large Ciliate Class Kinetofragmophora de Puytorac et al., 1974, and Recognition of Several New Taxa Therein, with Emphasis on the Primitive Order Primociliatida N. Ord". Journal of Eukaryotic Microbiology. 21 (2): 207–220. doi:10.1111/j.1550-7408.1974.tb03643.x.
^Gao, S; et al. (Nov–Dec 2008). "Phylogeny of six genera of the subclass Haptoria (Ciliophora, Litostomatea) inferred from sequences of the gene coding for small subunit ribosomal RNA". Journal of Eukaryotic Microbiology. 55 (6): 562–6. doi:10.1111/j.1550-7408.2008.00360.x. PMID19120803. S2CID41417127.
^Vd'ačný, Peter; et al. (May 2011). "Phylogeny and Classification of the Litostomatea (Protista, Ciliophora), with Emphasis on Free-Living Taxa and the 18S rRNA Gene". Mol Phylogenet Evol. 59 (2): 510–22. Bibcode:2011MolPE..59..510V. doi:10.1016/j.ympev.2011.02.016. PMID21333743.
