Choanozoa

Choanozoa are a group of eukaryotic organisms belonging to the superkingdom Opisthokonta. This group includes the choanoflagellates, which are considered the closest living relatives of the animals (Metazoa). Choanozoa are characterized by having a single flagellum surrounded by a collar of microvilli, structures that are used for feeding on bacteria and other small particles suspended in water. This unique feature is also found in the choanocytes of sponges, which are among the simplest animals, supporting the evolutionary relationship between choanoflagellates and metazoans.

Characteristics

Choanozoa are primarily aquatic and can be found in both freshwater and marine environments. They are unicellular or form simple colonies. The key characteristic that defines the Choanozoa is the presence of a flagellum encircled by a collar of microvilli, which is used for feeding. The movement of the flagellum creates water currents that draw food particles towards the cell, which are then captured and ingested by the microvilli.

Classification

The classification of Choanozoa has evolved over time with advances in molecular phylogenetics. They are currently placed within the Opisthokonta, a superkingdom that also includes animals, fungi, and several other groups. Within the Choanozoa, there are mainly two groups of interest:

• Choanoflagellates: These are the most well-known members of the Choanozoa and are considered to be the closest living relatives of animals. They provide key insights into the origin and evolution of multicellularity in animals.
• Filasterea: A less well-known group that includes a few species of amoeboid organisms. Filastereans are also closely related to animals and choanoflagellates and have been important in understanding the early evolution of the opisthokonts.

Evolutionary Significance

Choanozoa are of particular interest to biologists because they provide clues about the last common ancestor of all animals. The similarities between choanoflagellates and the choanocytes of sponges suggest that the earliest animals may have resembled these simple, filter-feeding organisms. Studies of choanoflagellate genetics and biology are helping scientists to reconstruct the steps that led to the evolution of multicellular organisms and the complex body plans seen in modern animals.

Research and Applications

Research on Choanozoa, especially choanoflagellates, has implications beyond evolutionary biology. Understanding how simple organisms like choanoflagellates regulate the formation of colonies and differentiate into specialized cell types can provide insights into the fundamental mechanisms of cell signaling and organization. This, in turn, has potential applications in medicine and developmental biology.

See Also

• Opisthokonta
• Eukaryote
• Multicellularity
• Animal Evolution