Cortical alveolum

Cortical alveoli have been defined as flattened membranous sacs or vesicles that strengthen the cellular cortex through the firm fixation to the underlying membrane and microtubules. They typically form a continuous layer that acts as a flexible film, although they can also constitute a semi-rigid structure or the scales of a theca. ==Occurrence==

Cortical alveoli are the defining morphological characteristic of the protist clade Alveolata, otherwise united solely by molecular phylogeny. In addition to the TSAR supergroup, the Archaeplastida supergroup contains a lineage of algae with cortical alveoli, known as Glaucophyta. All species of glaucophytes exhibit flattened membranous alveoli lying immediately below the plasma membrane, in every region of the cell except for the flagellar furrow. In addition, these alveoli may contain rigid plates that, similarly to thecate dinoflagellates, define the shape of the otherwise amorphous cell. Instead, both Archaeplastida and the TSAR supergroup are united in a clade known as Diaphoretickes, which contains the remaining chromist groups Haptista and Cryptista. == Function ==

Although cortical alveoli are very diverse in shape and function among the different groups of protists, they always share the function of supporting the cytoplasmic membrane. In the case of apicomplexan parasites, the alveoli are related both to mobility and to the invasion of host cells and thus have a particular relevance in medicine. In dinoflagellates, the alveoli contain cellulose and compose the scales of their armor. The alveoli of ciliates are part of the cortical complex that supports the extrusomes, the basal bodies of the cilia, and the intricate cortical shell. ==References==