Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
nătātĭlis, e, adj. [nato], that can swim (post-class.): animae, Tert. adv. Herm. 33.
Subst.: nătātĭles, ĭum, m., swimming creatures: feras, volucres, reptiles, natatiles, Prud. στεφ. 10, 332; App. de Mund. 28.