Extrusomes are membrane-bound structures in some eukaryote

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s which, under certain conditions, discharge their contents outside the cell. There are a variety of different types, probably not homologous, and serving various functions.

Notable extrusomes include mucocysts, which discharge a mucous mass sometimes used in cyst formation, and trichocyst

Trichocyst

http://media-2.web.britannica.com/eb-media/68/8968-004-A94DB3DF.jpg A trichocyst is a structure in the cortex of certain ciliate and flagellate protozoans consisting of a cavity and long, thin threads that can be ejected in response to certain stimuli...

s, which discharge a fibrous rod. The stinging nematocysts found in Cnidaria

Cnidaria

Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...

n animals may be regarded as extrusomes as well. Extrusomes found in dinoflagellate

Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

s are important in the formation of red and black tides.

External links

• Image: extrusome (labeled EX)