''Stentor'', sometimes called trumpet animalcules, are a genus of filter-feeding,

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

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, representative of the

heterotrich The heterotrichs are a class of ciliates. They typically have a prominent adoral zone of membranelles circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are ...

s. They are usually horn-shaped, and reach lengths of two millimeters; as such, they are among the largest known extant

unicellular organism 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 ...

s. They reproduce asexually through

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

Description

The body, or

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

, is generally horn-shaped, hence the association with the Greek herald, and the former name "trumpet animalcule". A ring of prominent

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

around the anterior "bell" sweep in food and aid in swimming. Some reach several millimeters in length, making them among the largest single-celled organisms. ''Stentor'' can come in different colors: for example, ''S. coeruleus'' can appear blue due to the presence of stentorin, a natural pigment. As in many freshwater protozoans, ''Stentor'' has a

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contractile va ...

. Because the concentration of salt inside the cell and in the surrounding freshwater is different, ''Stentor'' must store water that enters it by

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...

and then discharge it from the vacuole. They can regenerate, and small fragments can grow into full organisms. Each cell has one (often elongated)

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. During conjugation, t ...

and several

micronuclei Micronucleus is the name given to the small 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 i ...

. File:Mikrofoto.de-Stentor-1.jpg, ''Stentor polymorphus'' with algal symbionts File:Mikrofoto.de-Stentor-4.jpg, ''Stentor polymorphus'' with algal symbionts File:Dwa stentory.jpg, Stentors settled on water milfoil leaf

Ecology

These protists are common worldwide in freshwater lakes and streams; only ''S. multiformis'' has been recorded from marine, freshwater, and even terrestrial

biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. ''Biotope'' is almost synonymous with the term "habitat", which is more commonly used in English-speaking countrie ...

s. They are usually attached to algal filaments or detritus. Some ''Stentor'' species, such as ''S. polymorphus'', can live symbiotically with certain species of green algae (''

Chlorella ''Chlorella'' is a genus of about thirteen species of single-celled green algae belonging to the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain the ...

''). After being ingested, the algae live on while their host absorbs nutrients produced, whereas the algae, in turn, absorb and feed on the ''Stentor'' metabolic wastes. ''Stentor'' species react to outside disturbances by contracting into a ball. Resting cysts are known from a few species.

Systematics

The genus contains over twenty described species (see list in box). The genus ''Stentor'' was named in 1815 by the German biologist

Lorenz Oken Lorenz Oken (1 August 1779 – 11 August 1851) was a German naturalist, botanist, biologist, and ornithologist. Oken was born Lorenz Okenfuss (german: Okenfuß) in Bohlsbach (now part of Offenburg), Ortenau, Baden, and studied natural history and ...

(1779–1851). The

type species In 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 species that contains the biological type specimen ...

of the genus is ''Stentor muelleri'' Ehrenberg, 1831. According to recent molecular analyses, the genus seems to be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

, and related to the genus ''

Blepharisma ''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 ...

''.

Video gallery

References

External links

* * * *Tartar, Vance. (1961) ''The biology of Stentor''. New York, Pergammon Press. https://archive.org/details/biologyofstentor00tart {{DEFAULTSORT:Stentor (Protozoa) Heterotrichea Taxa described in 1815 Articles containing video clips Ciliate genera