Trichocyst


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trichocyst

[′trik·ə‚sist]
(invertebrate zoology)
A minute structure in the cortex of certain protozoans that releases filamentous or fibrillar threads when discharged.

Trichocyst

 

a type of extrusome; a cytoplasmic organelle of protozoans that is discharged when the protozoan is mechanically or chemically irritated.

Filamentous trichocysts are protective organelles typical of Infusoria; they are elongated (2–6 microns) albuminous bodies of paracrystalline structure. They generally have a dense tip and are situated in the cytoplasm perpendicular to the surface, as in par-amecia. When discharged, they extend into a filament 20–60 microns long and ending in a sharp point.

There are other types of trichocysts in infusorians, as follows. Mucoid trichocysts, or protrichocysts, are without a sharp point; they swell into a jellylike substance with a houndstooth pattern when discharged. Rhabdocysts are rod-shaped and are completely extruded to the surface of the protozoan. Toxicysts are poisonous organelles of predatory infusorians; they are used for attack and are generally located in a circumoral position. They consist of a long capsule containing a telescoping tubule that extends when discharged. Haptocysts are minute extrusomes located at the tips of antennae; they consist of an ampulla and a short tubule. Cnidocysts, or stinging capsules, are oval or spherical in shape. They contain a wound-up tubular filament that can unwind.

Mastigophorans have mucoid trichocysts, filamentous trichocysts, cnidocysts, and taeniobolocysts. The last is in the form of an albuminous rolled-up ribbon that unrolls when discharged. Cnidosporidians have cnidocysts (polar capsules), which are characteristic of spores. When cnidocysts are discharged, they help attach spores to the host’s body.

I. B. RAIKOV

References in periodicals archive ?
The ciliary patterns on the surface of the trophont are the basis for species identification among apostome ciliates (Chatton and Lwoff 1935), though other characteristics can be used to identify whether a ciliate is an apostome or not, including internal structures; especially trichocysts, secretory dense bodies, a rosette, and membrane organelles (Bradbury 1966, 1973, Landers 1991a, 1991b, Landers et al.
Paramecia can expose students to many organelles that they wouldn't normally have the opportunity to see, such as oral grooves, food vacuoles, cilia, macronuclei, and, in some cases, trichocysts.
The role of trichocyst discharge and backward swimming in escaping behavior of Paramecium from Dileptus margaritifer.