SITES OF PARTICLE SELECTION DETERMINED FROM OBSERVATIONS OF INDIVIDUAL FEEDING LARVAE OF THE SAND DOLLAR DENDRASTER-EXCENTRICUS

To determine where particles that differ in flavor are selected during feeding, I videotaped individual larvae of Dendraster excentricus while they fed from a mixed suspension of polystyrene beads of 10- and 20-mum diameter. A reciprocal treatment design that controlled for the effect of size consisted of flavoring one of the two particle sizes with exudate from an axenic culture of Dunaliella tertiolecta while the other remained unflavored. Analysis of gut contents showed that larvae preferentially ingested flavored particles (ANOVA, F = 17.10, P < 0.001). Analysis of videotaped larvae revealed selection at the ciliated band in two of the four experiments, although these did not always favor flavor. Clearance rate at the ciliated band was significantly higher than at the gut (ANOVA, F = 12.68, P = 0.004), and only 1-5% of particles were lost during transfer from the ciliated band to the mouth. The difference in clearance rate resulted from ejection of particles by the mouth and esophagus (the dominant site of selection) occasionally overriding selection at the ciliated band.