The peritrichs (Latin: Peritrichia) are a large and distinctive group of
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.
The peritrichs were first defined by
Friedrich von Stein
Samuel Friedrich Nathaniel Ritter von Stein (November 3, 1818 – January 9, 1885) was a German entomologist. He was Professor at the Royal Saxon Academy of Forestry in Tharandt from 1850–55; and Professor, and later Rector, at the Charles Uni ...
in 1859. Initially they were considered
spirotrich
The spirotrichs are a large and diverse group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down ...
s, then treated as a separate category, before receiving their modern placement.
Structure
They are usually bell or disc shaped, with a prominent
paroral membrane arising from the oral cavity and circling counter-clockwise around the anterior of the cell, accompanied by a smaller series of
membranelles. The oral cavity is apical and funnel shaped, with 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 ...
discharging directly into it. When disturbed, the anterior of the cell can contract. The rest of the body is unciliated, except for a ''telotroch band'' circling the posterior in mobile species and stages.
Order Sessilida
The larger order of Peritrichia are the
Sessilida. Most of these have modified posterior
kinetosomes which secrete a contractile stalk. The unattached stage, called a
telotroch, is mouthless. These are common in both freshwater and marine environments, and many live attached to aquatic plants and animals. They are either solitary or produce branched colonies. A few secrete a
lorica. ''
Vorticella'' is one of the best-known genera. Stalks may be as long as 2 mm, and in some cases where they are highly contractile can be extended up to 3 mm.
Order Mobilida
The other peritrichs make up the order
Mobilida
Mobilida is a group of parasitic or symbiotic peritrich ciliates, comprising more than 280 species. Mobilids live on or within a wide variety of aquatic organisms, including fish, amphibians, molluscs, cnidarians, flatworms and other ciliates, ...
. In these the posterior of the cell is enlarged and modified to form a complex holdfast, allowing the cell to temporarily attach to some host organism. Most live on the integument or gills of freshwater and marine invertebrates, but other hosts occur, including fish and even other ciliates, and other locations as well. Some can be pathogenic for fish.
References
Further reading
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External links
*http://eol.org/pages/2909715/entries/29157118/overview
*https://commons.wikimedia.org/wiki/File:20140728_Peritrichida.webm
Oligohymenophorea
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