Diffusoreids

Diffusoreids are a proposed clade of marine, single-celled eukaryotes distinguished by their porous, diffusion-oriented cell surfaces. The name derives from their hypothesized reliance on diffusive exchange of nutrients rather than traditional phagocytosis or complex ingestion mechanisms. Members are small, typically 5–25 micrometers in diameter, and are characterized by flexible, mesh-like outer membranes with numerous channels that connect the cell interior to the surrounding water.

Taxonomy and classification: Diffusoreids have been variably placed within protist groups that include nanoscale flagellates and filose eukaryotes. Molecular analyses, including small-subunit ribosomal RNA genes and transcriptomes, consistently identify Diffusoreids as a distinct lineage, but there is no broad consensus on their precise placement. Some classifications regard them as incertae sedis until more data are available.

Ecology and physiology: Diffusoreids inhabit nutrient-poor pelagic environments, including mesopelagic zones and nutrient-depleted gyres. They are primarily heterotrophic, feeding on dissolved organic matter and bacteria through surface diffusion and short, active protrusions. A few species appear to host endosymbiotic bacteria that may assist in nutrient processing.

Distribution and discovery: Known occurrences come from deep-sea sediments and plankton samples across the Atlantic, Indian, and Pacific Oceans. First described in recent metagenomic and single-cell surveys, researchers have yet to establish robust culture for this group, limiting controlled physiological experiments.

Significance: Diffusoreids highlight diversity in microeukaryote strategies for nutrient uptake and may shed light on early diffusion-based life forms. Ongoing molecular work aims to resolve their position in the eukaryotic tree and clarify their ecological roles in oceanic systems.