Apicomplexa

Apicomplexa is a phylum of single-celled eukaryotic parasites, including Plasmodium and Toxoplasma. Most use a specialized apical complex to invade host cells.

Apical complex: A group of specialized structures at the front of many apicomplexan cells that helps them attach to and enter host cells. Its secretory organelles and cytoskeletal structures give the phylum its name and enable cell invasion.
Alveolata: A major eukaryotic lineage characterized by membrane-bound sacs called alveoli beneath the cell surface. Apicomplexa belongs to this lineage alongside ciliates and dinoflagellates.
Malaria: A mosquito-transmitted disease caused by Plasmodium parasites, with fever and potentially severe complications. Plasmodium species cause malaria and illustrate the phylum's complex life cycles.
Ciliophora: A eukaryotic phylum of mostly single-celled organisms that move or feed using cilia. Ciliates share alveolate ancestry with apicomplexans but are generally not obligate parasites.
Gliding motility: A form of substrate-bound movement powered by an internal actin–myosin system, without visible cilia or flagella. Many apicomplexans use this movement to reach host cells and cross tissues.
Apicoplast: A nonphotosynthetic plastid found in many apicomplexans, descended from a photosynthetic ancestor. Its retained metabolic pathways provide drug targets despite the loss of photosynthesis.
Toxoplasmosis: An infection caused by Toxoplasma gondii, often mild but dangerous during pregnancy or in immunocompromised people. Toxoplasma gondii is a widely studied apicomplexan with broad host range.
Dinoflagellata: A diverse group of alveolate eukaryotes, many of which use two flagella and live in aquatic environments. Dinoflagellates are close alveolate relatives, but most differ in lifestyle and cellular form.
Moving junction: A transient interface between an invading parasite and host cell that advances over the parasite as it enters. It forms a gateway through which many apicomplexans pass during host-cell invasion.
Endosymbiotic theory: The explanation that some eukaryotic organelles originated when one cell lived inside another and became integrated. It explains the plastid ancestry underlying the apicoplast in many members of the phylum.

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