Effects of Oxygen Tension on Pumping, Filtration and Oxygen Uptake in the Ascidian Phallusia mammillat

Abstract

The effects of declining oxygen tension on pumping, filtration and oxygen uptake were studied simultaneously in Phallusia mammillata (Cuvier, 1815). Identical effects were observed on rates of pumping and filtration; these remaln constant until the oxygen tension (PO,) falls to a mean level of 119 mm Hg (concentration = 3.85 m1 021-') and then decrease. Below a PO, of 98 mm Hg (3.18 m1 0,l-') the rates decrease more rapidly and become more variable. No particular rhythms emerged. Below a p02 of 119 mm Hg, rapid and rhythmic variations in the diameter of the cloacal siphon produce a pseudorhythm. the mechanism of mucus formation is not affected down to a p02 of Filtering efficiency stays constant, with values of 77 to 79 O/o; 98 mm Hg. Below a mean p02 of 119 mg Hg - the critical tension - oxygen uptake decreases; P. mamm~llata fails to regulate oxygen consumption and becomes a 'conformer'.