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"In a series of studies, Mimi Koehl and her collaborators have looked at (among other things) the bristle-equipped appendages of tiny crustaceans [Daphnia], as in fig. 6.4. These creatures swim with such appendages, using them as paddles - with a lot of semistagnant water around each bristle, an appendage can serve as a paddle. The creatures also use such appendages as rakes, filtering edible particles from the water around them. That requires the passage of water between the bristles. Paddle or rake? The appendages look pretty much alike. What determines how one can be used is the Reynolds number at which it operates. Viscosity and density are givens; size and speed of motion provide the operative variables. Large and fast lets an appendage rake; small and slow promotes paddling." (Vogel 2003:124) Edit References

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