True, Methane is a greenhouse gas
I think the hydra lacks the specialized cells for touch and chemical detection. On the other hand earthworms have touch, light, vibration and chemical receptors along the entire body surface. Both of them are invertebrates (those animals without a backbone), they include insects, worms, jelly fish, spiders among other animals.
An artificial leaf could replicate photosynthesis but instead it would also be artificial which then produces hydrogen fuel that will be energy efficient and carbon neutral. hope this helps.
