Diversity of Protists I

Excavata is a diverse group of protists, including both chemoorganotrophic and phototrophic species.

The key groups include diplomonads, parabasalids, and euglenozoans.

Diplomonads like Giardia are characterized by two nuclei and mitosomes, which are underdeveloped mitochondria incapable of ATP production.

Parabasalids are anaerobic species with a parabasal body. Trichomonas is a prominent example, lacking mitochondria but containing hydrogenosomes, which generate ATP with hydrogen gas as a byproduct.

Euglenozoans are motile species having the ability to function as both chemotrophs and phototrophs.

Most species typically have two flagella, but only one is externally visible, emerging from an anterior flagellar pocket.

The representative example, Euglena, exhibits mixotrophy. It thrives in the presence of light, but an extended period of darkness can cause it to lose its chloroplasts and switch to a chemoorganotrophic mode of metabolism.