Spotted salamanders lay firm, globular egg masses in vernal pools, and many masses turn visibly green as the green alga Oophila amblystomatis colonises the jelly. The relationship benefits both sides: the alga photosynthesises using carbon dioxide and nitrogenous waste from the embryos, and the embryos develop faster and with better survival in the oxygen the alga releases.
Work published in 2011 went further, reporting algal cells inside the embryonic tissues and even within salamander cells. That makes this the only well-documented case of a photosynthetic symbiont living inside the cells of a vertebrate, and it raises the question of how the alga escapes an immune response.
The partnership is often described as the embryo doing photosynthesis, which overstates it. The salamander gains oxygen and possibly some fixed carbon from a resident alga; it does not itself photosynthesise. Both partners can also be raised without the other.