Holozoa

Holozoa is a eukaryotic clade comprising animals and their closest unicellular relatives. Its living members include animals, choanoflagellates, filastereans, and ichthyosporeans.

Opisthokonta: A major eukaryotic group that includes animals, fungi, and several unicellular lineages. Holozoa is nested within this broader group, alongside the fungal lineage.
Choanoflagellate collar: A ring of microvilli surrounding the flagellum of a choanoflagellate cell. Its resemblance to animal choanocytes illuminates shared feeding structures.
Animal origins: The evolutionary history and emergence of the animal lineage. Holozoa places animals among their closest living relatives for reconstructing that history.
Monosiga brevicollis: A single-celled choanoflagellate used in genomic studies of animal origins. Its genome provided an early detailed comparison between animals and unicellular relatives.
Metazoa: The clade of multicellular animals, distinguished from their unicellular relatives. Metazoa is the animal branch within Holozoa.
Cell adhesion: The binding of cells to one another or to surrounding materials. Adhesion-related proteins in unicellular relatives help trace the origins of animal multicellularity.
Last common ancestor of animals and choanoflagellates: The ancestral population from which animals and choanoflagellates diverged. Its traits can be inferred by comparing branches within Holozoa.
Salpingoeca rosetta: A choanoflagellate capable of living as single cells or forming multicellular rosettes. Its life cycle offers a model for studying transitions between unicellular and multicellular states.
Choanoflagellatea: A group of unicellular and colonial eukaryotes bearing a flagellum surrounded by a collar of microvilli. Choanoflagellates are among the closest living unicellular relatives of animals.
Cadherin: A family of calcium-dependent proteins that mediate cell-to-cell adhesion in animals and other eukaryotes. Cadherin-like proteins occur beyond animals, complicating accounts of their evolutionary origin.

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