Portfellida

Portfellida is a small, recently proposed clade of aquatic eukaryotes known from marine and freshwater sediments. It comprises unicellular to simple filamentous organisms that are primarily heterotrophic and thought to feed by osmotrophy and phagocytosis.

Members typically show flexible, non-walled cells with variable sizes from a few to tens of micrometers. Some cells bear posterior flagella or pseudopod-like extensions; cellular organization ranges from solitary to simple colonies. Reproduction occurs by binary fission; rare spore-like stages have been reported.

Portfellida has been detected in coastal muds, estuaries, and oligotrophic lakes, often in low-oxygen microhabitats. They participate in the decomposition of complex organic matter and form part of microbial food webs.

The taxonomic position of Portfellida is unsettled. Molecular studies frequently place it near the boundary of major eukaryotic supergroups, while others fail to resolve its relationships. Because cultured representatives are scarce, inferences rely heavily on environmental sequences and single-cell genomes.

The type genus is Portfellia; other described genera include Portfellimonas and Marportella. Due to limited specimens and incomplete character sets, Portfellida remains a provisional clade in need of further cultivation and genomic characterization to clarify its evolutionary affiliations and ecological roles.