The appendages of Daphnia are used for both paddling movement and filter feeding because they are equipped with bristles, allowing them to operate at different Reynolds numbers for different functions.

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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)

Book
Comparative Biomechanics: Life's Physical World, Second EditionJune 17, 2013
Steven Vogel

Journal article
Hairy little legs: Feeding, smelling, and swimming at low Reynolds numbersFluid Dynamics in BiologyJanuary 27, 2012
M. A. R. Koehl

Journal article
WHEN DOES MOTION RELATIVE TO NEIGHBORING SURFACES ALTER THE FLOW THROUGH ARRAYS OF HAIRS?August 2, 1994
Loudon C, Best B, Koehl M.

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