FEEDING IN THE FAIRY SHRIMP STREPTOCEPHALUS-PROBOSCIDEUS (FRAUENFELD)(BRANCHIOPODA, ANOSTRACA) .1. ASPECTS OF THE FEEDING BIOLOGY

At 25-degrees-C and in a suspension of about 1,000,000 carmine particl es per ml, the thoracopods of Streptocephalus proboscideus beat metach ronally with a frequency of about 4.3 Hz. The phase difference between successive thoracopods is about one-eighth of an oscillation. For eve ry particle concentration tested, retention time was lower in adult fe males (maximum 61 +/- 19 min, minimum 30 +/- 3 min) than in males (max imum 72 +/- 23 min, minimum 47 +/- 15 min) of equal size. The speed of transport through the gut was dependent on particle concentration; wi th increasing particle density, retention time decreased, but increase d again at the highest densities tested. The shortest retention time o f carmine particles was observed at a concentration of 1,000,000 parti cles per ml; for yeast and Selenastrum, this concentration was 100,000 cells per ml. At the latter concentration, maximum ingestion rate als o was observed. After 5 min, ingested particles were seen in the abdom inal region, where the speed of transport greatly decreased. In adults , no preference between algal species and yeast was observed. Instead, distinct particle size preferences were observed among different size classes. The maximum size of ingested glass spheres was 17.2 mum in l arvae and 67.1 mum in adults, probably a function of the size of the m outh.