Jakobacells are found as naked freeswimming trophic cells in marine environments.

Trophic cells are ellipsoidal to slightly pear-shaped (the latter usually when the cells are compressed, as under a cover slip; or, when well fed, as in the picture) and between 5 and 10 micrometers long. Two flagella emerge from the anterior end of the cell. The anterior flagellum is free; at rest, the flagellum often projects anteriorly at first and then "hooks back" ventrally. The posterior flagellum normally remains in a groove that runs longitudinally along the ventral surface of the cell, usually all the way to the posterior end. The groove is defined by a cytoplasmic vane on the right ventral side of the cell. Bacteria are captured in the ventral groove and are digested in food vacuoles. Cells swim in straight lines, rotating along their longitudinal axes. They may also "squirm" along a surface.

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