Filter feeding in lancelets (amphioxus), Branchiostoma lanceolatum

Little work has been done to describe lancelets as filter feeders, and hith erto no data have existed on either filtration rates or the efficiency with which food particles are retained in the filters. The aim of the present w ork was to describe and characterize Branchiostoma lanceolatum as a true fi lter-feeding species. The:clearance-rate capacity in B. lanceolatum was mea sured at naturally low algal concentrations, and used as a reference state representing the normal filtration rate in nature and for comparisons with video recordings of the feeding currents. Simultaneous measurements of clea rance different-sized particles, prepared as a mixture of flagellates (Isoc hrysis, Rhinomonas, and Tetraselmis) showed that particles greater than or equal to 4 mu m are retained by the mucus filter with 100% efficiency.,The wavelength and speed of the metachronal wave of the lateral cilia, which ge nerates the power of the branchial pump, were measured to estimate the cili ary beat frequency. Furthermore, transport rate, production, exposure time, and flow speed of water through the mucus filter was estimated. The loss o f body dry-weight during a long term starvation period was used as an indir ect measure of the respiration rate. The results are used to characterize f ilter feeding in B. lanceolatum a way that may be compared to a number of o ther macro-invertebrate filter feeders that have been studied during recent years.