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cytostome
A cytostome (cyto- meaning cell and stome- meaning 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 vacuoles.
Only certain groups of protozoa, such as the ciliates and excavates, have cytostomes.〔Allaby, Michael. A dictionary of zoology. Oxford University Press, 2003.〕 Such examples include ''Balantidium coli'' - a ciliate. In others, and in cells from multicellular organisms, phagocytosis takes place at any point on the cell or feeding takes place by absorption.
== Structure ==
The cytostome forms and invagination on the cell surface and is typically directed towards the nucleus of the cell.〔Okuda, Kendi, et al. "The cytostome of Trypanosoma cruzi epimastigotes is associated with the flagellar complex." Experimental parasitology 92.4 (1999): 223-231.〕 The cytostome is often labeled as the entire invagination, however this is a misnomer; the cytostome only constitutes the opening of the invagination at the surface of the cell. The rest of the invagination is classified as the cytopharynx.〔Preston, T. M. "The Form and Function of the Cytostome‐Cytopharynx of the Culture Forms of the Elasmobranch Haemoflagellate Trypanosoma raiae Laveran & Mesnil." The Journal of protozoology 16.2 (1969): 320-333.〕 The cytopharynx works in conjunction with the cytostome in order to import macromolecules into the cell. This strong association between the cytostome and cytopharynx is often called the cytostome-cytopharynx complex or the cytopharyngeal apparatus. However, in a small number of cases the cytostome works independently in order to import macromolecules. In these instances, the cytostome imports macromolecules by directly forming vesicles that are imported into the interior of the cell.〔
The cytostome is associated with microtubules that function in maintaining its form. One set of microtubules is arranged in a triplet formation and is located directly beneath the cytostome membrane. A second set of microtubules is positioned directly beneath the flagellar pocket membrane and forms a quartet.〔Alcantara, Carolina L., et al. "The three-dimensional structure of the cytostome-cytopharynx complex of Trypanosoma cruzi epimastigotes." Journal of cell science 127.10 (2014): 2227-2237〕
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