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 whi le they fed from a mixed suspension of polystyrene beads of 10- and 20 -mum diameter. A reciprocal treatment design that controlled for the e ffect of size consisted of flavoring one of the two particle sizes wit h exudate from an axenic culture of Dunaliella tertiolecta while the o ther remained unflavored. Analysis of gut contents showed that larvae preferentially ingested flavored particles (ANOVA, F = 17.10, P < 0.00 1). Analysis of videotaped larvae revealed selection at the ciliated b and in two of the four experiments, although these did not always favo r 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 parti cles were lost during transfer from the ciliated band to the mouth. Th e 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.