I know this is late but if I recall correctly Abathur is orginally designed as a giant monstrosity of Zerg on Heart of the Swarm concept art book , most of his body is hidden within the tunnel of evolution pit on that leviathan. He is in fact, a giant worm-centipede like creature, where is bottom part under the tunnel is way way way bigger than his upper “torso” and with many really really creepy legs (the one that pop off on evolution pit r in fact his leg, stretching from below). He also somehow managed to live on Char completely hidden when Overmind died and Hive clusters went wild and start rampage on their own. I assumed he is either really good at hiding or the worse, he manage to eat those who find him. As far as in HotS it can be simply explained as he can “detach” himself from that lower part like the Xenomorph queen from Alien vs Predator.
All primal zerg are pretty much that; adapt, change, survival of the fittest, betrayal, take advantage of others to become the dominant life form in their crazy, ageless evolutionary playground. Swarm zerg may be considered tyranid-lite (practically the same other than their motivation and zerg being "younger"... as well as a little faster in their whole invasion process), but primal zerg would fit right in with Tzeentch.
Any primary Core Leaders have been too much to see these interactions with Abathur were all generic, because that is Evolution Master belongs to Kerrigan's Swarm, some of it (like Li-Ming and Cassia) took against Kerrigan, Abathur have been not only focuses Kerrigan but also to others.
