I'm glad you enjoyed Deepest Known, as I found that song really fun to work on (well, the whole thing was, but I'd say Deepest Known and Biolumenesca were particularly enjoyable for me.). We wanted the very bottom of the sea floor to feel large and imposing, but maybe not so scary if you look at it with the right angle. We wanted it to remain still, but not feel lifeless. After all, as inhospitable as such an environment might be to most creatures, it's still got plenty of it's own life adapted to it.
What we ended up with was a track in Locrian (for maximum darkness) as well as writing the base of the song in 1/1. However, for each new layer of the song added, we increment that layer's meter up a step. So it begins by adding a layer of 2/2 over top of the 1/1 base, then 3/4 over all that, then 4/4, 5/4, etc... Ultimately culminating in a ten time signature poly-meter once the final 10/4 percussion is established. Zoe compared this to the pressure of the deep ocean growing more and more.
None of the layers have more than a single bar long phrase on their own, and thus cannot progress the song in a natural way like typical songs would, which serves to keep the musical progression feeling still.
But throughout all of this, we really didn't want it to be boring to listen to, which was a fear I had while initially thinking about the song. So we added in the poly-meters and tried our best to make sure that each layer felt distinct enough & filled out their own role in the song. The bass-line likes to mimic the most recently introduced pattern and steals it's time signature each time after listening to it for a bit, which Zoe mentioned was inspired by Cuttlefish and other mimicry-based ocean animals, which I find to be really cute concept.
In the end, I'd describe the song's progression as more of a rhythmic and groove-based one rather than a more traditional melodically-based progression, which I ultimately think is fitting, as it allows the song to progress in it's own different, more alien way, much like one might think of the kinds of animals that reside at such insane depths as the hadopelagic zone of the ocean, so different from anything most other life on Earth is used to.
Making the song really made me appreciate how great poly-meters are at creating natural variations between bars since their phrases never end up lining up with each-other the same way every time they play alongside each-other. Anyways, I kind of went on a tangent here! Ultimately, I'm glad you enjoyed the soundtrack and I appreciate your comment a lot. Thanks!