I always imagined it as the mutant xenos version of the hive resin we saw in aliens/alien but as these xenos are mutated the resin is more organic and alive than the resin we saw in the earlier movies and the tails and xeno limbs we see is just the resin recreating some xeno parts.
Like corporal hicks said: I would loved to see more of their hive and how different it must had been compared to what true xenos hives are like. Like show us the queen aliens egg chamber before she escaped and maybe some facts and how she could escape with her state at that time, and all facehugged hosts, if they even had some? More why they had several of the doctors cooccooned in the queens room but still not facehugged, are they all alive or are some of them dead as none of them speaks besides Wren?
Oh well so much potential to fascinating facts but they missed it.