Discocilia and Paddle Cilia in the Larvae of Mulinia lateralis and Spisula solidissima (Mollusca: Bivalvia)

¹ Institute of Oceanology, University of Valparaiso, P.O. Box 13-D, Vina del Mar, Chile
² Virginia Institute of Marine Science, School of Marine Science, The College of William and Mary, Gloucester Point, Virginia 23062

The bivalve larval velum contains four bands of cilia: inner and outer preoral bands, an adoral band, and a postoral band. The preoral bands of compound cilia are generally considered to be used for both locomotion and food gathering. The adoral and postoral bands function in concert with the preoral bands in food gathering and transfer of food to the mouth. Cilia are usually described as cylindrical structures which taper to a blunt tip. Modified cilia with disc-shaped (discocilia) or paddle-shaped ends have been recorded in several invertebrate species. Here, for the first time, we demonstrate the presence of discocilia in the velum of Mulinia lateralis and paddle cilia in the velum of Spisula solidissima. Such cilia are restricted to the preoral bands and the central ciliary tuft. The presence of such cilia does not appear to increase the swimming velocity of these larvae in comparison to that of Rangia cuneata larvae of similar size. The possibility that these modified cilia have enhanced sensory capability remains to be tested.