The rate of transportation of granules (mitochondria) within the pseudopodia was studied in seven sublittoral foraminiferan species from the west coast of Sweden: Astrorhiza limicola, Cornuspira foliacea, Crithionina granum, Globipelorhiza sublittoralis, Phainogullmia aurata, Quinqueloculina seminulum and Technitella legumen. The average organelle velocity was found to increase with temperature in all species. Five of these species showed a similar increase of velocity (about 2–4 μm/s at 2 °C, to about 6–8 μm/s at 17 °C). The velocity of Quinqueloculina seminulum, however, increased far more than the others at high temperatures (9–12 μm/s at 17 °C), while the velocity of the komokiacean Globipelorhiza sublittoralis was far less than all others at all temperatures (about 2 μm/s at 2 °C to 4 μm/s at 13 °C). The increased pseudopodial organelle velocity is interpreted to reflect an increased metabolism and consequently an increased demand for the exchange of oxygen, waste products, and material through the pseudopodial membrane. The much branched granuloreticulose pseudo-podial network increases the respiratory surface many-fold. We suggest that this is a factor allowing the extreme increase in cell size in foraminiferans.