''Blepharisma'' 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 ...

protists A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...

found in fresh and salt water. The group includes about 40 accepted species, and many sub-varieties and strains. While species vary considerably in size and shape, most are easily identified by their red or pinkish color, which is caused by granules of the pigment blepharismin. All members of the genus possess a long series of

membranelle Membranelles (also membranellae) are structures found around the mouth, or cytostome, in ciliates. They are typically arranged in series, to form an "adoral zone of membranelles", or AZM, on the left side of the buccal cavity (peristome). The membra ...

s on the left side of the oral groove, and an "undulating membrane" (a structure resembling a flap, scarf or small sail, composed of long cilia fused together as a single sheet) on the right side of the

peristome Peristome (from the Greek language, Greek ''peri'', meaning 'around' or 'about', and ''stoma'', 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Some plants, fungi, and shelled gastropods have peristomes. In mo ...

, toward the posterior. Certain species of ''Blepharisma'' have served as

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

s for scientific research. Since some varieties are easily cultured and readily available from scientific supply houses, they are a common object of study in school science classes.

Appearance

''Blepharisma'' may be as small as 50 micrometres in length, or as large as 1 mm (though normal size range is between 75 and 300 micrometres). Body shape varies within the genus. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of the genus, ''B. persicinum,'' is ellipsoidal. ''Blepharisma lateritium'' is teardrop-shaped, with a rounded posterior; while ''Blepharisma elongatum'' and ''Blepharisma sphagni'' are long and thin, tapering at the posterior into a tail-like point. All species are uniformly ciliated, with the cilia arranged in longitudinal rows, and stripes of pigment alternating between rows of cilia. Cilia, short hairlike organelles, sweep food into its mouth and are used for movement. The pink or red pigmentation may be quite pale, and in certain cases it is absent altogether. 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 ...

, often quite large, is located in the posterior. The

Macronuclei 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 ...

can take a variety of forms. Depending on species and phase of life, they may be rod-shaped, ovoid, spherical, or moniliform (like a rosary, or string of beads).

Reproduction and sexual phenomena

Like all ciliates, ''Blepharisma'' reproduce asexually, by

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 ...

, dividing transversally. Fission may occur spontaneously, as part of the vegetative

cell cycle The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell (biology), cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA re ...

, or it may follow a sexual phenomenon called

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 ...

, a process through which genetic material is exchanged between cells. In conjugation, two organisms come into close contact, and a temporary cytoplasmic bridge forms between them. The

micronuclei A micronucleus is a small cell nucleus, nucleus that forms whenever a chromosome or a fragment of a chromosome is not incorporated into one of the daughter nuclei during cell division. It usually is a sign of genotoxic events and chromosomal inst ...

of each cell then undergo

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

, and

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

micronuclei pass from one individual to the other. This permits the reshuffling of hereditary characteristics, as in other types of

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

. Conjugation is immediately followed by binary fission of the two conjugants. In ''Blepharisma'', as in some other ciliates, chemical substances called gamones are used to induce conjugation by stimulating interaction between compatible mating partners. Although clonal cells of ''Blepharisma'' are sometimes able to conjugate with one another (a phenomenon known as

selfing Autogamy or self-fertilization refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species of ...

),Miyake A. (1981). Cell interaction by gamones in Blepharisma In: Sexual Interactions in Eukaryotic Microbes (O’Day, D.H. editor), pp. 95-129 New York: Academic Press. conjugation ordinarily involves the interaction of cells of different mating types. In the species ''Blepharisma japonicum'', there are two mating types (I and II), each type excreting a specific pheromone (termed gamone 1 and gamone 2, respectively). When sexually mature mating-type I cells are moderately starved, they autonomously produce and secrete gamone I. Gamone 1 specifically acts on mating-type II cells, transforming them so that they can unite with type I cells, and inducing them to secrete gamone 2. Gamone 2 then transforms type I cells so that they can unite with type II cells. Cells that can unite may then undergo conjugation. Conjugation of opposite mating types promotes

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing in animals Out ...

and the masking of deleterious recessive mutations in the diploid phase of the sexual cycle.

Feeding and behavior

''Blepharisma'' feed on a variety of smaller organisms, including

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

, flagellate algae,

rotifer The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic Coelom#Pseudocoelomates, pseudocoelomate animals. They were first describ ...

s, other ciliates and even smaller members of the same species. Experiments with ''Blepharisma undulans'' have shown that cannibalism causes gigantism. When individuals are given a diet of smaller ''Blepharisma'', or certain ciliates (particularly ''

Colpidium colpoda ''Colpidium colpoda'' are free-living ciliates commonly found in many freshwater environments including streams, rivers, lakes and ponds across the world. ''Colpidium colpoda'' is also frequently found inhabiting wastewater treatment plants. This ...

'' or ''

Tetrahymena ''Tetrahymena'' is a genus of free-living ciliates, examples of unicellular eukaryotes. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. ''Tetrahymena'' cel ...

''), they grow to a relatively enormous size. As long as their diet remains unchanged, cannibal giants will divide to produce more giants. When large prey become unavailable, the offspring will revert to normal size.

Photobiology

''Blepharisma'' are markedly photophobic, and when light levels are increased will seek out darkened areas. The ability to detect light is accomplished with photosensitive pigment granules located just under the

plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

of the cell. The pigment in these granules is

blepharismin ''Blepharisma'' is a genus of unicellular ciliate protists found in fresh and salt water. The group includes about 40 accepted species, and many sub-varieties and strains. While species vary considerably in size and shape, most are easily ident ...

, the same substance that gives ''Blepharisma'' their characteristic pinkish color. ''Blepharisma'' are usually pink when collected in nature, but when grown in darkness with abundant food they turn red. Exposure to light or starvation causes them to lose their color, but deeply-pigmented cells can even be killed by strong light.

List of species

* '' B. americanum'' Suzuki, 1954 * '' B. bimicronucleatum'' Villeneuve-Brachon 1940 * '' B. bothrostoma'' Mermod 1914 * '' B. botezati'' Lepsi, 1926 * '' B. coeruleum'' Gajevskaja, 1927 * '' B. caudatus'' Dumas 1937 * '' B. clarissimum'' Kahl, 1928 * '' B. dawsoni'' Christie & Hirshfield 1967 * '' B. dileptus'' Kahl, 1928 * '' B. elegans'' Vuxanovici 1963 * '' B. elongatum'' (Stokes, 1884) Kahl, 1926 * '' B. falcatum'' Gelei 1954 * '' B. galianoi'' Fernandez-Leborans 1979 * '' B. grayi'' Hartwig & Parker, 1977 * '' B. halophila'' Ruinen 1938 ** Found to be a phylogenetic outlier under the

orthographical variant In biology, within the science of Nomenclature, scientific nomenclature, i.e. the naming of organisms, an orthographical variant (abbreviated orth. var.) in botany or an orthographic error in zoology, is a spelling mistake, typing mistake or writi ...

''Blepharisma halophilum''. * '' B. hyalinum'' Perty, 1852 * '' B. intermedium'' Bhandary, 1962 * '' B. ichthyoides'' V. Gelei, 1933 * '' B. japonicum'' (Suzuki, 1954) Giese, 1973 * '' B. lateritium'' (Ehrenberg, 1831) Kahl, 1932 * '' B. lentis Gelei'' 1954 * '' B. melana'' Borror, 1963 * '' B. minima'' Lepsi, 1926 * '' B. multinucleata'' Dragesco, 1960 * '' B. musculus'' Penard, 1922 * '' B. ovalis'' Dumas 1937 * '' B. ovatum'' Penard, 1922 * '' B. parasalinarum'' Dragesco 1997 * '' B. persicinum'' Perty, 1849 * '' B. salinarum'' Florentin, 1899 * '' B. seshachari'' Bhandary, 1962 * '' B. sphagni'' Lepsi, 1926 * '' B. steini'' Kahl, 1932 * '' B. tardum'' Kahl, 1928 * '' B. undulans'' Stein, 1868 * '' B. velatum'' Vacelet, 1961 * '' B. vestitum'' Kahl, 1928 * '' B. violaceae'' Tucolesco 1962 * '' B. vitreum'' Lepsi 1957 * '' B. wardsi'' Hirshfield, Isquith & Bhandary, 1965

Appearance

Reproduction and sexual phenomena

Feeding and behavior

Photobiology

List of species

References

Further reading