Feeding mechanism and house of the appendicularian Oikopleura vanhoeffeni

Abstract

Although the feeding apparatus of oikopleurid Appendicularia has been described in general, functional details of the feeding mechanism and fluid mechanical constraints on the feeding process remain unknown. My goals were to determine the number of mucous-net layers in the feeding filter of Oikopleura vanhoeffeni collected from March 1985 to February 1986, and to describe the pathway of water flow through the filter. Marker particles (i.e. Isochrysis galbana, carmine, charcoal powder, and starch), and rhodamine dye were added to the natural food suspension to help in visualizing structure and flow. The feeding filter was composed of three layers. Water flowed into the filter through two large, lateral openings at the base of each wing, and along the open distal margins of the filter. Under hydrostatic pressure generated by the tail, water moved through the filter in a one-way bulk flow and was forced through the mucous mesh of both the dorsal and ventral layers. Thus, the feeding filter concentrated the food suspension by sieving most of the incoming water. The filter did not collect or trap food particles. Because of its function, I propose calling the feeding filter the “food concentrating filter”.