choanomonads

Choanomonads are a group of flagellated protists, typically marine or freshwater, characterized by a unique collar of microvilli surrounding a single anterior flagellum. This collar structure is highly distinctive and plays a crucial role in their feeding mechanism. The beating flagellum creates a water current that draws food particles, such as bacteria and dissolved organic matter, towards the cell. These particles are then trapped by the microvillar collar and ingested by the cell.

Choanomonads are often solitary, but some species can form colonies. Their reproductive strategies vary, including asexual division. They are considered ecologically significant as filter feeders, contributing to the control of microbial populations in aquatic environments.

The morphology of choanomonads has led to their recognition as the closest living relatives of metazoans (animals). Their collar cells, known as choanocytes, are the fundamental cell type found in sponges, an early-branching group of animals. This evolutionary connection highlights the ancient origins of multicellularity and the cellular mechanisms that underpin animal life. The study of choanomonads provides valuable insights into the early evolution of animals and the development of complex feeding structures.