My speculation is (since all animals picked seem to share a vage aspect of the way the jobs wour in pvp)
Dark knight, crab, I suspect they will be high armored but vunerable while attacking, much like crabs greatest weapon their claws are also their most vunerable point.
Mechanist, iguana, marksmen of nature, different branch than bird
Astrologist, butterfly or more likely moth, just because those are generally associated with astral/mysticism.
