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 slze and f ~ b e r diameter of the food-concentrating fllter were determined for cornpanson with similar measurements on larger oikopleurids from cold ocean waters. The filter was con~posed of 3 types of fibers arranged In a regular rectangular array. In accordance with nomenclature used previously, we identified microfibers, nodulated fibers, and smooth fibers There were dense nodes where microfibers and nodulated fibers crossed. Mean pore size was 0.15 + 0.02 X 0.61 + 0.13 ,um ( t SD), with a mean wtdth-to-length ratio of 0.25 f 0.03 and mean porosity of 0.85 + 0.01. Mean pore size is sim~lar to that of O~kopleura djoica, a temperate-ocean oikopleund of similar body size, but is smaller than that of Oikopleura vanhoeffeni, a large, cold-ocean oikopleund. The rnicrof~bers of 0. longicauda were 17.1 f 2 6 nm in diameter, while the nodulated fibers were 38.9 t 8.8 nm in diameter, and the smooth fibers 48.1 f 10.2 nm in d~amete r All 3 fiber types formed branches, which contributed to high variance of mean pore slze.