Anderson, E. J., MacGillivray, P. S. and M. E. DeMont. 1997. Scallop shells exhibit optimization of riblet dimensions for drag reduction. Biological Bulletin 192: 341-344.

Boats and automobiles have known to be modified to enhance performance, one such modification often being the addition of ribs to increase aerodynamic properties. Is it possible that Placopecten magellanicus, a scallop known for its propulsive swimming abilities, displays this very same type of optimization?

Many scallops (Family Pectinidae) have the ability to swim using a type of "jet-propulsion". By trapping water when the shells of the bivalve open and then rapidly shutting the shells, streams of water are expelled propelling the scallop in a gape-first direction, sometimes allowing predator escape and possibly seasonal migration. P. magellanicus, as well as other scallops, display longitudinal ribs that run from gape to hinge. Such ribs may reduce drag by streamlining vortices that would normally add turbulence (wall shear stress).

hell lengths and rib spacing were measured for 16 genera that demonstrated similar riblet dimensions to P. magellanicus in order to determine the rib spacing that delivered optimal swimming performance. In addition, film of in situ swimming was observed to obtain swimming velocities of the scallops. Using mathematical formulas to calculate wall shear stress, results indicated that at smaller shell lengths (less than 40 mm) rib spacing fell out of optimum range, while larger shells, like the 50 mm shell of P. magellanicus, demonstrated rib-spacing that led to the greatest swimming speeds.

In conclusion, P. magellanicus apparently does display a functionally significant role in its observed ribs, as they allow for drag reduction and therefore, greater swimming ability.

(248 words)

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(posted Mar. 24 2009)