Presumably, Xindus was class M; the Enterprise crew had no issues with Xindi-breathable atmospheres, and Reptilian troops could board Enterprise without breathing equipment.
or it could be class L. Or Xindi are just resiliant in class M atmospheres. Note that of the Xindi-occupied planets actualy seen only the Arboreal colony seems no-brainer match for a class M planet, and it wasn't settled for the climate. In short, this note seems a bit too speculative. -- Capricorn 22:25, December 12, 2009 (UTC)