Aphelida
Aphelida are intracellular parasites that infect algae and other protists. They are an early-diverging opisthokont lineage closely related to fungi.
Aphelidium: A genus of aphelid parasites that infects algal cells. Its life cycle illustrates how an aphelid enters and develops within an algal host.
Opisthokonta: A major eukaryotic group that includes animals, fungi, and several unicellular lineages. Aphelida belongs to this broad lineage of eukaryotes.
Molecular phylogenetics: The study of evolutionary relationships using comparisons of molecular sequences. Sequence analyses established aphelids as a distinct, deeply branching opisthokont lineage.
Host–parasite interaction: A biological relationship in which a parasite benefits while living on or within a host, which is harmed. Aphelid infection is a direct example of a parasite exploiting a unicellular host.
Aphelidium protococcarum: An aphelid species that parasitizes the green alga Coccomyxa. This species is a studied example of intracellular development in an algal host.
Holomycota: The opisthokont lineage comprising fungi and their closest unicellular relatives. Aphelids are placed among the deep branches near the fungal side of opisthokont evolution.
Fungal evolution: The evolutionary history of fungi and the lineages most closely related to them. Aphelids help clarify which traits may have preceded the origin of fungi.
Algal bloom: A rapid increase in the abundance of algae in an aquatic environment. Parasites of algae can influence the growth and persistence of algal populations.
Zoospore: A motile, usually flagellated reproductive cell produced by certain protists, fungi, and algae. Aphelid zoospores locate hosts and initiate infection.
Fungi: A kingdom of eukaryotes that includes yeasts, molds, and mushrooms, typically absorbing nutrients from their surroundings. Aphelida is a close relative of fungi, though aphelids are parasites rather than conventional fungi.