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1 Committee on Evolutionary Biology, University of Chicago, Chicago, Illinois 60637
2 Department of Geology, The University of Akron, Akron, Ohio 44325-4104
3 Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois 60637
* To whom correspondence should be addressed, at Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013-7012. E-mail: hunte{at}si.edu
Despite the diversity and ecological importance of cypridoidean ostracodes, there have been no kinematic studies of how they swim. We used regular and high-speed video of tethered ostracodes to document locomotion in the cypridoidean species Cypridopsis vidua. Swimming in this species is drag-based, with thrust provided by both antennulae and antennae. About 15 complete power and recovery strokes occur per second; maximal speeds for the limb tips were about 30 mm/s for the antennulae and 50 mm/s for the antennae. These speeds correspond to Reynolds numbers on the order of 101 to 100 for the limb tips and 102 to 101 for the setae that extend outward from the swimming limbs and provide much of the surface area of the limb. The strokes of the four thrust-producing limbs are coordinated in a manner that seems to be unique among aquatic arthropods. When viewed from the anterior, power strokes are synchronized diagonally: left antennula and right antenna power strokes start at the same time and terminate just as the power strokes for the right antennula and left antenna begin. Because power strokes occur throughout the stroke cycle, swimming in this species is smoothly continuous, without the rapid accelerations and decelerations characteristic of most small aquatic arthropods.
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