Comparison of the ultrastructure of the food-concentrating filter of two appendicularians

Abstract

Houses of Oikopleura longicauda were removed from preserved zooplankton samples and prepared for transmission electron microscopy. Pore size and fiber diameter of the food-concentrating filter were determined for comparison with similar measurements on larger oikopleurids from cold ocean waters. The filter was composed of 3 types of fibers arranged in a regular rectangular array. In accordance with nomenclature used previously, microfibers, nodulated fibers, and smooth fibers were identified. There were dense nodes where microfibers and nodulated fibers crossed. Mean pore size was 0.15 plus or minus 0.02 x 0.61 plus or minus 0.13 mu m ( plus or minus SD), with a mean width-to-length ratio of 0.25 plus or minus 0.03 and mean porosity of 0.85 plus or minus 0.01. Mean pore size is similar to that of O. dioica , a temperate-ocean oikopleurid of similar body size, but is smaller than that of O. vanhoeffeni , a large, gold-ocean oikopleurid