This is an unusual example of a Shell Galaxy
Shell galaxies happen when a pair of galaxies are attracted directly toward each other (or as in this case, very nearly so)
Cores are very dense, VERY massive objects but there is still plenty of room between stars for two cores to pass through each other.
All that mass created very strong attraction which increased rapidly as they neared, creating tremendous momentum.
The large momentum kept them moving forward until it was overcome by gravitational attraction again.
Rinse & repeat with ever smaller momentums until the two nuclei merge or, as we see here, they shift to a crazy death spiral.
The point is that at every vector change the galaxies leave inertial, or centrifugal, imprints of stars left behind - thus the shells.
See Two merging galaxies are simulated as an n-body system with a total of 150,000 particles
Also, see NGC 3923
https://www.legacysurvey.org//viewer/?ra=177.7491&dec=-28.7984&layer=ls-dr10&zoom=11