All free-living & exclusively marine.

All free-living. Many tardigrade species are found on bryophytes (mosses, liverworts, and hornworts) and leaf litters that are moist and humid, the ideal limno-terrestrial environment for these microanimals. Tardigrades are also known to be extremely hardy. Should the environment become unfavorable to live in, most species are capable of entering a "tun" state which renders them virtually indestructible - capable of withstanding extreme temperature and pressure at either end of the spectrum, radiation, hypoxia, starvation, and even desiccation.