Swimming speed and Reynolds numbers of eleven freshwater rotifer species

We obtained data on the swimming speed of 11 freshwater rotifer species. These data were analyzed in terms of Reynolds numbers given the fact that rotifers are in the evolutionary boundary between the use of cilia and swimming appendages. Swimming speed ranged from 0.174 to 0.542 mm ^–1. Philodina acuticornis odiosa was the fastest rotifer in terms of absolute speed. However, Gastropus hyptopus, the smallest of the rotifers analyzed, was the fastest (2.849) in terms of body-lengths s^–1. Reynolds numbers (Re) among the 11 species analyzed varied from 0.023 to 0.301. Lecane furcata had the smallest Re, while Epiphanes senta had the highest Re. The two bdelloid rotifers analyzed in this work swam five times faster than they crept. The importance of Reynolds numbers and drag coefficients are discussed in view of the present results and data found in the literature.