Schematic illustration of O₂ distribution in the internal and external environments of <i>Osedax mucofloris</i>.

<p>A: <i>Osedax mucofloris</i> extend its palps and pinnules, with large respiratory surfaces, into the overlying O₂-rich water in order to uptake O₂. O₂ is then distributed to the buried root system through the extensive blood vascular system also supplying the heterotrophic endosymbionts. The O₂ distribution to the root system is crucial as local uptake is not possible in the anoxic bone environment. The anoxic environment is partly produced by intense bacterial processes (green arrows) utilizing O₂ at the bone surface. Hydrogen sulphide is produced by anoxic bacterial processes within the bone matrix during decomposition of organic content using sulphate. B: Schematic illustration of assumed blood flow in palp and pinnules, longitudinal section. Blue vessels carrying venous blood through afferent vessels, red vessels carrying arterial blood through efferent vessels. C: Schematic illustration of assumed blood flow in palp and pinnules, transverse section. Likewise blue vessels carries venous blood through afferent vessels, red vessels carries arterial blood through efferent vessels. Note that the palp blood vessels are created by an invagination of the basement membrane. Green indicates musculature.