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. 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. 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. 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.