[8] Jakobids have two flagella, inserted in the anterior end of the cell, and, like other members of order Excavata, have a ventral feeding groove and associated cytoskeleton support.

[9] The posterior flagella has a dorsal vane and is aligned within the ventral groove, where it generates a current that the cell uses for food intake.

[6] The sessile, loricate Histionidae and occasionally free-swimming Jakoba libera (Jakobidae) have extrusomes under the dorsal membrane that are theorized to be defensive structures.

[6][11] Some are capable of surviving hypersaline and anoxic environments, though the Histionids have only been found in freshwater ecosystems, where they attach themselves to algae or zooplankton.

[4][6] Their primary prey is generally considered to be bacteria, though one species has been observed eating extremely small (< 1 μm) eukaryotic cells.

[6] Jakobid mitochondrial DNA is substantially different from most other eukaryotes, especially in terms of the number of genes (nearly 100 in some species) and bacteria-like elements within their genomes.

[6] Another hypothesis is that the phage-type RNA polymerase moved from one eukaryote group to another via lateral gene transfer, replacing the bacteria-type enzyme, and simply did not reach the Jakobids.

[6] However, the gene arrangement of Jakobid mitochondrial DNA suggests an ancestral origin of bacteria-type RNA polymerase over a more-recent divergence.