''Vorticella'' is a genus of bell-shaped

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a differen ...

s that have stalks to attach themselves to substrates. The stalks have contractile myonemes, allowing them to pull the cell body against substrates. The formation of the stalk happens after the free-swimming stage.

Etymology

The organism is named ''Vorticella'' due to the beating cilia creating whirlpools, or vortices. It is also known as the “Bell Animalcule” due to its bell-shaped body.

History

''Vorticella'' was first described by Antonie van Leeuwenhoek in a letter dated October 9, 1676. Leeuwenhoek thought that ''Vorticella'' had two horns moving like horse ears near the oral part, which turned out to be oral cilia beating to create water flow. In 1755, German miniature painter August Johann Rösel described ''Vorticella'', which was named ''Hydra convallaria'' by Linnaeus in 1758. However, in 1767, it was renamed ''Vorticella convallaria''. Otto Friedrich Müller listed 127 species of ''Vorticella'' in 1786, but many are now known to actually be other protozoans or rotifers. The definition of ''Vorticella'' that is still used today was first given by Ehrenberg in 1838. Since then, 80 more species have been described, although many may be synonyms of earlier species.

Habitat and ecology

Habitats may include moist soil, mud and plant roots. This protozoan is ciliated and is mainly found in fresh water environments. They are known to feed on bacteria and can also form extracellular associations with mosquitoes, nematodes, prawns and tadpoles. ''Vorticella'' has been found as an epibiont (attached to the surface of a living substratum when in its sessile stage) of crustaceans, the basibiont. This relationship between the epibiont and basibiont is called epibiosis. Rotifers have been observed to feed on ''Vorticella''. Bacteria found on the bodies of ''Vorticella'' may be parasites.

Description

These solitary organisms have globulous bodies which are oval-shaped when contracted. Unfavourable conditions tend to cause ''Vorticella'' to change from long and skinny to short and wide. The oral cavity is at one end while the stalk is at the other. The body is 30-40 micrometers in diameter contracted and the stalk is 3-4 micrometers in diameter and 100 micrometers long. The protoplasm of ''Vorticella'' is typically a translucent blue-white colour, but may contain a yellow or green pigment. The food vacuoles may show as a brown or grey colour, but depends on the food eaten.

Zoochlorella ''Zoochlorella'' is a ''nomen rejiciendum'' for a genus of green algae assigned to ''Chlorella''. The term zoochlorella (plural zoochlorellae) is sometimes used to refer to any green algae that lives symbiotically within the body of a freshwater ...

e, food reserves and waste granules, which are abundant in the cytoplasm, may create the impression that ''Vorticella'' is an opaque cell. ''Vorticella'' has a pellicle with striae running parallel around the cell. This pellicle may be decorated with pustules, warty projections, spines or tubercules. Harmless or parasitic

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

may grow on the body or stalk, appearing as part of the morphology of the cell. Inside, there is a curved, transverse

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 conjugati ...

and round

micronucleus 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 ...

near it.

Stalk

During its motile form, the free-swimming telotroch appears as a long cylinder, moving quickly and erratically. Stalk materials are secreted in order for the cell to become sessile. Stalk precursors are held in dense granules at the aboral or basal end of the telotroch, which are released as a liquid by

exocytosis Exocytosis () is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell ('' exo-'' + ''cytosis''). As an active transport mechanism, exocytosis requires the use ...

. That liquid solidifies to form the adhesion pad, stalk matrix and stalk sheath. The stalk will finish growing in several hours. The stalk is made up of the spasmoneme, a contractile organelle, with rigid rod filaments, batonnets, surrounding it. The coiled spasmoneme and batonnets serve as a molecular spring, so that ''Vorticella'' can contract. The cell body can move hundreds of micrometers in milliseconds. The spasmoneme is said to have higher specific power than the engine of the average car.

Feeding

''Vorticella'' has an anterior peristomial lip which is short and narrow. An outward-curving peristomial disc is associated with the peristome. The peristomial disc, which may have ringed ridges or undulations, encloses rows of cilia. The contractile peristomal border closes over the disc and cilia during retraction of ''Vorticella''. ''Vorticella'' is a suspension feeder, and may have reduced or no cytopharynxes, a nonciliated tube for ingestion. There are oral cilia specialized for making water currents, cytostomes in a depression on the cell surface and structures for scraping and filtering food. Oral cilia beat to bring food closer at speeds of 0.1–1 mm/s. Water flowing inwards brings food through the vestibule, between the inner and outer membranes. The vestibule is a passage for both food entrance and waste exit. The vestibular membranes push the food inwards, where they then congregate in a spindle-shaped

food vacuole The food vacuole, or digestive vacuole, is an organelle found in simple eukaryotes such as protists. This organelle is essentially a lysosome. During the stage of the symbiont parasites' lifecycle where it resides within a human (or other mammali ...

in the pharynx. Once the food vacuoles leave the non-ciliated pharyngeal tube, they become rounded. When the water flows outwards, contractile vacuoles and full food vacuoles may empty their contents. Contractile vacuoles are located between or beside the macronucleus and vestibule. The oral cilia contain the adoral zone of membranelles (AZM), which are compound ciliary organelles. The paroral membrane consists of a row of paired cilia. The

cytostome 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 ...

has the AZM on one side and the paroral membrane on the other side. As adults, they do not have somatic cilia. In terms of reproduction, ''Vorticella'' can undergo binary fission. This occurs when the organism splits into two parts, with the division going along the length of the organism (“The ''Vorticella''” 1885).

Fossil history

A fossil ''Vorticella'' has been discovered inside a leech cocoon dating to the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

period, ca. 200 million years ago. The fossil was recovered from the Section Peak Formation at Timber Peak in East

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

, and has a recognizable peristome, helically-contractile stalk, and C-shaped

, like modern ''Vorticella'' species.

''Vorticella'' as pest control

The growth, development and emergence of mosquito larvae are inhibited by ''Vorticella'', resulting in death. The biopolymer glue used for attachment to surfaces may damage sensory systems or pore formation of larvae. Another possibility is that the larvae die by being unable to remain on the surface of the water, thus drowning. ''Vorticella'' has for this reason, been explored as a method of biocontrol for mosquitoes, which are vectors of pathogenic, tropical diseases.

Systematics

Over 200 species of ''Vorticella'' have been described, although many may be synonyms.

Molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

shows that some species that were previously considered to be ''Vorticella'' because of their morphology actually belong to another group, forming a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

with the swimming peritrichs '' Astylozoon'' and '' Opisthonecta''.

Common species

*'' Vorticella aequilata'' *'' Vorticella campanula'' *'' Vorticella chlorostigma'' *'' Vorticella citrina'' *'' Vorticella convallaria'' **'' Vorticella convallaria compacta'' *'' Vorticella elongata'' *'' Vorticella fusca'' *'' Vorticella gracilis'' *'' Vorticella lima'' *'' Vorticella mayeri'' *'' Vorticella microstoma'' (not a true ''Vorticella'', according to molecular phylogeny) *'' Vorticella natans'' *'' Vorticella oceanica'' *'' Vorticella similis'' *'' Vorticella striata ''