What features, in addition to maximizing surface area, are necessary to optimize the intake of CO2 and H2 for a sessile, multicellular methanogenic organism?
This organism lives at depths of 10 kilometres around hydrothermal vents, converting CO2 and H2 into H2O and CH4. Sessile, it acquires gases from the surrounding ocean and those emitted from the seafloor. Ranging from 10 cm to 1 m in diameter, this organism exists in an environment dominated by others of its species resembling tightly packed barnacles without shells.
The planet is purely composed of vast oceans with no land or elevated seafloors. Due to the low energy yield from the CO2 and H2 reaction and the early stages of evolution, the planet is undergoing, efficient predatory adaptations haven't evolved yet
An organ under the skin distributes the gases to the cells. Or an open circulatory system