A question about 'reptiles and volatiles' to describe creatures

The words that you are looking for are natatile (for fish) and gressile (for land animals).

The Oxford English Dictionary (OED) has entries for both adjectives, defined as "Able to swim; swimming" and "Able to walk" (via cross-reference to the synonym gressible). The OED entry for gressile includes the following citation that illustrates the parallel usage with volatile and reptile:

1659 D. Pell Πελαγος 193 Terrestrial. And under this term I would comprehend, 1. Gressile, 2. Volatile, 3. Reptile.

Gressile is mentioned also in the Dictionary of Early English, by Joseph T. Shipley (1955):

gressile, gressive; gressorial; adapted for walking. The simple forms from the Latin hardly survive in English (cp. couth), but we still use many compounds [...] Terrestrial creatures may be classified as walking, flying, or crawling: gressile, volatile, or reptile.

("gressible", p. 315)

Both adjectives are classified as "obsolete" by the OED, as is the "Birds, esp. wild-fowl." sense of the word "volatile". Regardless, if you're using volatile in the sense of "flying" and reptile in the sense of "creeping", those seem to be the usual terms used to complete this set of Latinate -ile adjectives for modes of animal motion. If you're not looking for these words, I don't understand the question.

Both words can be found alongside volatile and reptile in a Latin quotation from Gassendi in the book On Certain Modified Forms assumed by the Inductive Process in Different Sciences, by Robert Mortimer Glover (1837), p. 13.

Natatile is from the Latin verb nato "swim", and gressile is from the Latin verb gradior "walk" (the same gress as in the word progress).