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 particles per ml, the thoracopods of Streptocephalus proboscideus beat metachronally with a frequency of about 4.3 Hz. The phase difference between successive thoracopods is about one-eighth of an oscillation. For every particle concentration tested, retention time was lower in adult females (maximum 61 +/- 19 min, minimum 30 +/- 3 min) than in males (maximum 72 +/- 23 min, minimum 47 +/- 15 min) of equal size. The speed of transport through the gut was dependent on particle concentration; with increasing particle density, retention time decreased, but increased again at the highest densities tested. The shortest retention time of carmine particles was observed at a concentration of 1,000,000 particles per ml; for yeast and Selenastrum, this concentration was 100,000 cells per ml. At the latter concentration, maximum ingestion rate also was observed. After 5 min, ingested particles were seen in the abdominal 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 larvae and 67.1 mum in adults, probably a function of the size of the mouth.