Didinium
Encyclopedia
Didinium is a genus
of ciliophora. They are free-living carnivores, mostly found in fresh and brackish water
environments, although at least three marine species
are known. Their diet consists primarily of Paramecium
, but some species such as D. gargantua feed on other protist
s including dinoflagellate
s, cryptomonad
s, and green algae.
bands, called pectinellae, encircling the organism. This distinguishes them from the related genus Monodinium, which only have a single band except during cell division
. The pectinellae are used to move through water by rotating
the cell around its axis. Didinium are rounded, oval, or barrel-shaped and range in length
from 40 to 200 µm. At the anterior
end, a cone-shaped structure protrudes which encloses the cytostome
or "mouth" opening, as found in other haptoria
n ciliates. The dimension of cone varies among the different species. The nucleus
may also appear curved in an arched, U-shape. Didinium reproduce
via binary fission asexually
, or sex
ually via conjugation. A didinium moves by beating its cilia.
, D. nasutum, employs specialized structures called toxicysts (some sources refer to these structures as trichites) to ensnare and paralyze
the ciliary movement of its prey, Paramecium. Once captured, the Paramecium, is engulfed whole by D. nasutum through its anterior cytostome.
In the absence of its Paramecium prey, D. nasutum will encyst, lying dormant
within a protective coating
. The cyst
s have been shown to remain viable for at least 10 years. When the cyst form of D. nasutum is exposed to its exclusive Paramecium food source it will excyst. At least one laboratory
study showed that other conditions can trigger encystment in D. nasutum, such as the build-up of excessive waste
products in the environment and other stimuli.
containing the gene
s passed from generation
to generation and a "somatic" macronucleus
within each organism. Products of conjugation
, micronuclear meiosis
and fusion to form the zygote
are followed by mitotic
division and the formation of a macronucleus. Throughout this complex process the chromosome
s undergo many processes that affect their composition, making phylogenetic analysis more difficult. In fact, at least two articles conclude that the Haptoria are not a monophyletic
group.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of ciliophora. They are free-living carnivores, mostly found in fresh and brackish water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
environments, although at least three marine species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
are known. Their diet consists primarily of Paramecium
Paramecium
Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...
, but some species such as D. gargantua feed on other protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s including dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...
s, cryptomonad
Cryptomonad
The cryptomonads 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 anterior groove or pocket...
s, and green algae.
Structure
Didinium have two ciliaryCilium
A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....
bands, called pectinellae, encircling the organism. This distinguishes them from the related genus Monodinium, which only have a single band except during cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
. The pectinellae are used to move through water by rotating
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
the cell around its axis. Didinium are rounded, oval, or barrel-shaped and range in length
Length
In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...
from 40 to 200 µm. At the anterior
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
end, a cone-shaped structure protrudes which encloses the cytostome
Cytostome
A cytostome 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 vacuoles. Only certain groups of protozoa, such as the ciliates and excavates, have cytostomes. Such...
or "mouth" opening, as found in other haptoria
Litostomatea
The Litostomatea are a class of ciliate protists. Until recently, the class Litostomatea was divided into two groups, the Haptoria and the Trichostomatia. However, new genetic information has resulted in the resurrection of a third subclass, Rhynchostomatia, first proposed by A. W. Jankowski in...
n ciliates. The dimension of cone varies among the different species. The nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
may also appear curved in an arched, U-shape. Didinium reproduce
Biological reproduction
Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction...
via binary fission asexually
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, or sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
ually via conjugation. A didinium moves by beating its cilia.
D. nasutum
Much of what is described for this genus is based on the extensive studies of a single species, Didinium nasutum. A voracious predatorPredation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, D. nasutum, employs specialized structures called toxicysts (some sources refer to these structures as trichites) to ensnare and paralyze
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
the ciliary movement of its prey, Paramecium. Once captured, the Paramecium, is engulfed whole by D. nasutum through its anterior cytostome.
In the absence of its Paramecium prey, D. nasutum will encyst, lying dormant
Dormant
Dormant means lacking activity. It can refer to:*Dormancy in an organism's life cycle*Dormant volcano, a volcano that is inactive but may become active in the future...
within a protective coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
. The cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s have been shown to remain viable for at least 10 years. When the cyst form of D. nasutum is exposed to its exclusive Paramecium food source it will excyst. At least one laboratory
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...
study showed that other conditions can trigger encystment in D. nasutum, such as the build-up of excessive waste
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...
products in the environment and other stimuli.
Phylogenetic analysis
Phylogenetic analysis of the ciliates has presented a challenge to researchers due to the presence of both a "germ line" micronucleusMicronucleus
A the micronucleus is the smaller nucleus in ciliate protozoans, such as the paramecium. In fission it divides by mitosis, and in conjugation furnishes the pairing of gamete nuclei, by whose reciprocal fusion a zygote nucleus is formed, which gives rise to the macronuclei and micronuclei of the...
containing the gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s passed from generation
Generation
Generation , also known as procreation in biological sciences, is the act of producing offspring....
to generation and a "somatic" macronucleus
Macronucleus
A macronucleus is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, the everyday tasks, such as metabolism...
within each organism. Products of conjugation
Bacterial conjugation
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells...
, micronuclear meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
and fusion to form the zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
are followed by mitotic
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
division and the formation of a macronucleus. Throughout this complex process the chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s undergo many processes that affect their composition, making phylogenetic analysis more difficult. In fact, at least two articles conclude that the Haptoria are not a monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
group.