''Nassula'' 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, belonging to the class

Nassophorea The Nassophorea are a class of ciliates. Members are free-living, usually in freshwater but also in marine and soil environments. The mouth is anterior ventral and leads to a curved cytopharynx supported by a prominent palisade of rods or ''ne ...

. Like other members of the class, ''Nassula'' possesses a basket-like feeding apparatus (''nasse'', or '' cyrtos'') made up of cytopharyngeal rods (''nematodesmata''), which are themselves composed of closely packed

microtubules 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 nm and have an inner diameter between 11 an ...

. ''Nassula'' use this structure to ingest

filamentous cyanobacteria Cyanobacterial morphology refers to the form or shape of cyanobacteria. Cyanobacteria are a large and diverse phylum of bacteria defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis. Cyanobacteria ...

, drawing individual strands of blue-green algae through the

cytopharynx 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 ...

and into the body of the cell, where they are digested. As the algae are broken down, they can take on a variety of bright colours, which give ''Nassula'' a distinctive, variegated appearance under the microscope.

Description

The body is ovoid to elongate, and uniformly ciliated, with a single macronucleus and a partial hypostomial frange (''synhymenium'') running from the left side of the cell to the oral aperture. When food is scarce, members of the genus have the ability to become dormant by forming a

microbial cyst 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. ...

. Excystment can be induced by exposure to a medium inoculated with wild bacteria.

Reproduction

''Nassula'' reproduce asexually, by

fission Fission, a splitting of something into two or more parts, may refer to: * Fission (biology), the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Nuclear fissio ...

. During reproduction, the cell is divided transversally. As in most ciliates (with the exception of the

Karyorelictea Karyorelictea is a class (biology), class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, ''Lox ...

) 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 (, ...

splits, during division, and 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 ...

also undergo

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

. While fission is an asexual process, it may be preceded by

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 ...

, during which compatible mating individuals come together and transfer genetic material across a cytoplasmic link. In conjugation, the micronuclei of each cell 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 are then exchanged from one cell to the other. After sexual exchange has occurred, both conjugants will divide by fission.

Video gallery

Species list

References

{{Taxonbar, from=Q6967689 Nassophorea Ciliate genera Articles containing video clips Taxa named by Christian Gottfried Ehrenberg