> There is a worm that gets its food solely from
> symbiotic algae. However, sunlight on a human's body
> isn't nearly enough energy for us. Besides, we enjoy
Both solvable: increase the surface (unfoldable photosynthetic wings) and reassign the reward system so that basking is at least as fullfilling as an opulent meal. (If the sun doesn't shine, just plug yourself in into the wall socket, and fix carbon dioxide from air. Or refuel yourself with methanol).
Of course one should also get rid of the gastrointestinal system, reengineering the tissue so that we don't need to rely on bacterial symbiontes.
Yeah, it's silly, much better to immediately to go to dry (active transport, no solvent) postbiological systems altogether. Something relatively small, a swarm of redundant crab/spiderlike units, with lots of sensors/limbs and really speedy locomotion. And/or large, nuke-driven (a big carrier unit for the smaller systems, ranging from mosquito to gorilla size).